MT184CP

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. Ge rätebau, B a rsbüttel, Germany 10/2008

Teaching material

Dipl.-Ing. Klaus-Jürgen Radtke Dipl.-Geogr. Uta Linke

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Wherever liquids are transported, produced or required to be supplied, pumps are deployed. The demands which they must met vary widely. A vast range of fluids has to be conveyed, from highly sensitive pharmaceuticals, through large volumes of cooling liquid in power stations, to viscous chemical products.

A wide variety of pumps have been developed over time for industrial applications.

Not all pumps are mentioned in the following. Our outline presents a structured guide to the most common types of pump.

Code Product

MT 180 Assembly and maintenance exercise - centrifugal pump

MT 181 Assembly and maintenance exercise - multi-stage centrifugal pump MT 182 Assembly and maintenance exercise - screw pump

MT 183 Assembly and maintenance exercise - diaphragm pump MT 184 Assembly and maintenance exercise - piston pump

MT 185 Assembly and maintenance exercise - in-line centrifugal pump MT 186 Assembly and maintenance exercise - gear pump

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2.1 Classification and categorisation of pump types based on operating

principle

Pumps are fluid-flow machines which dictate how processes operate - that is to say, they ensure that flow takes place within systems.

In practice, pumps are often named after the liquid they pump or their purpose, such as milk pumps or cooling pumps. However, technicians and fitters can more easily identify their design when they are named according to their operating principle.

Fig. 2.1 Pump types Oscillating

Self-priming (Displacement

device moves back and forth along an axis)

Normally priming (Not carrying gas, pumping from low level restricted) Rotating

Self-priming (Displacement device rotates in

the pump body)

Self-priming (Carrying gas, pumping from low

level possible) Piston pumps Diaphragm pumps Centrifugal pumps Multi-stage centrifugal pumps Inline pumps Gear pumps Screw pumps Side-channel pumps Positive-displacement pumps (Medium conveyed by displacement device) Centrifugal pumps (A gyro causes centrifugal forces to act

on the medium) Engines (Flowing medium drives machine) Turbines Machines (Machine drives a flowing medium) Pumps Fluid-flow machines

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2.2 Designs and operating characteristics

The following table sets out the designs and operating characteristics of the most common positive-displacement pumps.

The piston pump incorporates an oscillating piston which is routed into a cylinder. The piston moves on an axis. The pump body is blocked by intake and pressure valves. A stroke gear drives the piston, which enlarges or reduces the pump chamber on every stroke.

By enlarging the pump chamber, the pumped fluid is drawn in by way of the intake valve. After a change of stroke the pump chamber is reduced and the pumped liquid is displaced by way of the pressure valve.

The diaphragm pump contains an elastomer

diaphragm which is clamped into the pump housing. The oscillation is transferred from the stroke gear to the diaphragm by way of a thrust rod. The fluid feeds in and out by way of the valves, frequently executed as ball valves.

The method of operation is the same as the piston pump, with the diaphragm acting as the displacement device.

The gear pump contains two opposite rotating rigid or elastic gear wheels. The pump body is not closed off by valves.

The liquid is pumped by the rotating gear wheels from the intake to the delivery side in the gaps between the teeth along the pump wall. The gear meshing and narrow gaps between the rotor and housing minimise the reflux.

The screw pump consists of two or more spindles with helical splines which rotate inside a correspondingly shaped housing. The pump body is not closed off by valves.

The liquid is pumped axially in the free screw turns from the intake to the delivery side.

Here too, as in the case of the gear pump, the sealing from the delivery to the intake side is provided by narrow gaps.

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The following table sets out the designs and operating characteristics of the most common centrifugal pumps.

The centrifugal pump contains a rotating, enclosed impeller with backward facing blades. The intake port is axially aligned to the pump shaft. The delivery port is aligned radially upwards.

The rotating impeller inside the pump body causes centrifugal forces to act on the pumped liquid. The liquid thrown out to the circumference of the pump by this flows out of the pump through the delivery port.

The multi-stage centrifugal pump is similar in design and action to the centrifugal pump. The difference is that is features multiple impeller arranged in a row on a shaft. The pumped liquid passes from the intake port via the rotating impeller through a fixed guide channel to the next impeller, and so on, until it reaches the delivery port. The multistage impeller layout means the pump attains higher delivery heads.

The inline centrifugal pump is similar in design and method of operation to the centrifugal pump. Its intake and delivery ports are along one axis however, though here too the feed to the pump flows axially by way of an appropriately shaped housing. The inline pump is used in straight pipelines.

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Other special centrifugal pump designs

The side-channel pump contains a rotating starshaped open impeller with radially running vanes. It rotates inside a pump housing featuring a side channel which narrows from the inlet to the outlet.

The energy transfer acts on the medium by means of an exchange flow of the liquid in the impeller with that in the side channel. The side channel pump thus operates continuously with a self-priming effect, whereas the centrifugal pump is not self-priming.

The canned motor pump is similar in design and action to the centrifugal pump. It is leakage-free, as it requires no shaft seal. The drive of the canned motor pump is located practically inside the pump housing, and the pumped liquid flows around it.

The magnetic clutch pump is similar in design and action to the centrifugal pump. It is leakage-free and requires no shaft seal.

The magnetic clutch pump is driven by a non-contact magnetic clutch. The magnet on the pump shaft is inside the pump housing. It is separated from the magnet on the motor shaft by a tube.

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2.3 GUNT Practice Line kits and their usage

The GUNT Practice Line kits for assembly and maintenance exercises include the following pumps:

MT 180 – Centrifugal pump

Centrifugal pumps are in widespread use, and are primarily used to pump fluid media. Their applications include in shipbuilding, industry and water supply.

Fig. 2.2 Toolkit with parts set and pump

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MT 181 – Multi-stage centrifugal pump

The multi-stage centrifugal pump is modular in design, and is used to pump fluid media at higher delivery pressures. It is used in water supply and in industry.

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. Ge rätebau, B a rsbüttel, Germany 10/2008 MT 182 – Screw pump

Screw pumps are primarily used to transport viscous media such as lubricat-ing oil, plant oil, glycols and polymers. Their applications include lubrication systems for diesel engines and transmissions, as well as in hydraulic systems.

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. Ge rätebau, B a rsbüttel, Germany 10/2008 MT 183 – Diaphragm pump

Diaphragm pumps are absolutely leakage-free and, provided appropriate materials are selected, are particularly well suited to pumping aggressive fluids such as acids and caustic in chemical engineering applications. Diaphragm pumps are often used for volumetric metering, as metering pumps.

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. Ge rätebau, B a rsbüttel, Germany 10/2008 MT 184 – Piston pump

Piston pumps are used primarily to transport fluids at high delivery pressures and low flow rates. Typical applications include pumping drinking water and domestic water in residential areas, in agriculture, onboard ships and in industry.

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MT 185 – Inline centrifugal pump

In-line centrifugal pumps are a sub-category of centrifugal pumps. Inline pumps are installed in straight pipelines. They are required in applications including water supply, watering and sprinkler systems, and in heating engi-neering.

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. Ge rätebau, B a rsbüttel, Germany 10/2008 MT 186 – Gear pump

Gear pumps are of the rotating positive-displacement pump category, and are characterised by pulsation-free delivery at operating pressures up to 40bar. High-viscosity media such as oils, paints and adhesives can be pumped.

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2.4 Operating characteristics of pumps

Alongside preventive maintenance, repair work forms a key part of general service operations. Damage to pumps can be traced back to incorrect oper-ation in more than 50% of cases.

It is advantageous for the assembly personnel to have basic knowledge of how the pump operates and are aware of how to use the pump correctly.

2.4.1 Pump and system characteristics

The delivery capacity of a pump is indicated by the pump’s characteristic curve. The delivery rates are measured on the test stand at the respective delivery pressures. The pump measurement data is depicted in the form of a characteristic curve. Usually the delivery head is given in place of the deliv-ery pressure (as a result the characteristic curves of centrifugal pumps are not dependent on the density of the pumped liquid).

In the case of centrifugal pumps the dependency of the delivery rate on the head is marked: As the head rises, the delivery rate decreases significantly. By contrast, the delivery rate of positive-displacement pumps remains virtu-ally constant as the head rises.

In the case of positive-displacement pumps, it must be ensured that the permissible operating pressure is not exceeded. Overflow valves are frequently used for this.

Fig. 2.16 Characteristic curve for a centrifugal pump

Fig. 2.17 Characteristic curve for a positive-displacement pump Delivery Q Delivery Q Head H Head H

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Operation of the positive-displacement pump with the overflow valve (partially) open is depicted in the horizontal segment of the curve (see Fig. 2.17).

The graph gives an indication of the delivery capacity of the pumps, though it provides no information on the delivery data actually achieved.

An often cited problem when operating pumps is that the pump does not reach the necessary pressure. Generally speaking, pumps only deliver mate-rial; the associated pressure is caused by the system.

The system operating data can likewise be measured and depicted graphi-cally in the system characteristic curve. As the delivery rate increases, the system pressure - determined by practical calculation - rises.

Fig. 2.18 System characteristic curve Delivery Q

Head

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. Ge rätebau, B a rsbüttel, Germany 10/2008 2.4.2 Operating point

The actual delivery data result from the interaction of the pump and the system.

If the pump and system curves are plotted on the same diagram, the point at which the curves intersect is the operating point.

So if the operating data do not conform to the specification, the technician should first check and calculate the correct operation of the pump in the system. This should be done on initial commissioning and every time the system is modified.

Fig. 2.19 Operating point (1) of a normally priming centrifugal pump

Fig. 2.20 Operating point (1) of a positive-displacement pump Delivery Q Delivery Q Head H Head H 1 1

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2.4.3 Alteration of the operating point by restriction and variation of speed

In practice, restriction is frequently used to set the desired delivery rate. The flow is restricted by partially closing a valve on the delivery side of the pump. This results in a new system curve with a steeper rise. The new operating point 2 is the point of intersection of the new system curve with the pump curve. Or in other words: The operating point has shifted along the pump curve from 1 to 2.

While the delivery rate decreases as the head rises on a centrifugal pump, the delivery of a positive-displacement pump remains constant as the pressure rises.

Fig. 2.21 Shift in operating point from (1) to (2) by restriction for a normally priming centrifugal pump

Fig. 2.22 Shift in operating point from (1) to (2) by restriction for a positive-displacement pump Delivery Q Delivery Q Head H He ad H 1 2 2 1

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A common method of shifting the operating point of a pump is to vary the speed. The speed is varied by means of an adjuster gear or a frequency inverter. This produces a new pump characteristic curve.

The diagrams show an increase in speed from n₁ to n₂ for both pump types (see Fig. 2.23 and Fig. 2.24). In the case of the centrifugal pump, the pump curve moves upwards, while for the positive-displacement pump it shifts to the right.

In both diagrams the operating point shifts upwards along the system curve. That is to say, higher heads and delivery rates are produced as the speed increases.

Fig. 2.23 Influence on the pump characteristic of a variation in speed for a normally priming centrifugal pump

Fig. 2.24 Influence on the pump characteristic of a variation in speed for a

positive-displacement pump Delivery Q Delivery Q Head H Head H n₁ n2 n₁ n₂

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2.4.4 Operating characteristics of multiple interacting pumps

Operation of multiple pumps simultaneously in a system is quite common, and in many cases essential in order to conform to extreme operating speci-fications.

If multiple pumps are configured in parallel, the delivery rate is increased. If pumps are configured in series (one behind the other), the delivery heads are added together.

The pump industry has made use of these properties and developed a number of designs accordingly.

Multi-flow pumps achieve high delivery rates, multi-stage pumps achieve high heads.

Fig. 2.25 Parallel configuration Fig. 2.26 Series configuration

Fig. 2.27 Multi-flow pump, sectional view and delivery principle

Fig. 2.28 Multiple-stage pump, sectional view and delivery principle

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2.4.5 Intake characteristics of pumps

Attention must be paid to the intake characteristics of the pumps. A distinc-tion is made between selfpriming and nonselfpriming pumps.

The normally priming centrifugal pump is a non-self-priming pump. It is not capable of pumping a gaseous medium out of the pump body. It must always be ensured that a liquid is fed in from a higher level, or where the feed is from a lower level, the liquid head does not collapse, such as due to the use of foot valves on the intake side.

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Self-priming pumps include side channel pumps (see chapter 2.2, page 5). They are capable of pumping gases. However, the pump body must always be filled with liquid for this to happen. That is why the intake and delivery ports on side channel pumps always point upwards.

Most positive-displacement pumps are self-priming. The displacement device is able to compress the gas and displace it out of the pump body. For this to happen, however, the pump must be partially filled with liquid, because only wetted valves close exactly such that no reflux is possible. This also applies to rotating positive-displacement pumps, of which the wetted gaps restrict reflux.

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3 Basics of pump maintenance 23

3 Basics of pump maintenance

3.1 Definition Maintenance

All pump operators should maintain their pumps in accordance with the main-tenance and operating instructions issued by the manufacturers. Mainte-nance is the umbrella term for inspection, servicing and repair (see Fig. 3.1). A log book or machine file should be set up for each pump unit, indicating the current status and the repair work carried out to date.

Fig. 3.1 Maintenance

Replacement, Correction

With the system running and at stand

still based on inspection instructions

Only with the system stopped, based on specific work order and after careful preparation Only with system stopped according to maintenance instructions MAINTENANCE TO DIN 31051

Inspection Servicing Repairs

Recording and assessment of the current actual status

Restoration of the specified status Preservation of the specified status Measurement, Testing, Diagnosis Cleaning, Lubrication, Adjustment

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3.2 Reasons for maintenance

Pumps are required for the operations of many manufacturing systems. If the pumps are malfunctioning, there is a risk of production outages. Appropriate maintenance is a key factor determining the productivity of operations. Complete replacement of the pump is possible in the event of a defect, though it is not always essential and, especially, is not necessarily cost-effec-tive. Carrying out preventive maintenance and servicing, as well as repairs, is advantageous. A number of reasons are cited by way of example.

• The cost of purchasing a mid-sized industrial pump is considerable. The annual cost of wearing parts amounts to around 10% - 20% of the purchase price of the new pump.

• Holding a complete replacement pump in stock is inefficient and expensive for many businesses. It is, however affordable, and advisable, to hold stocks of key pump spares.

• The delivery lead times for complete pumps are usually lengthy, whereas spares can be supplied from suppliers’ central stores at short notice.

• Fig. 3.2 shows that routine maintenance of pumps (2) results in lower costs in the medium and long term than complete replacement of pumps (1).

Fig. 3.2 Total cost, comparison of replacement (1) and maintenance (2) Service life

Cos

t 1

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. Ge rätebau, B a rsbüttel, Germany 10/2008 3.3 Detection of faults

Many factors need to be considered in order to ensure optimised, trouble-free operation of pumps. Nevertheless, faults will routinely occur. A number of basic points need to be observed in order to assess faults and their causes: • The specifications of the delivery medium need to be considered in order

to ensure long service life of the pumps. The material durability of the pump components and seals must be ensured. The design and construc-tion of the pump must be attuned to the specific pumping requirements. • Most pumps are driven by electric motors. Attention must be paid to

correct dimensioning and selection.

• Incorrect electrical connections and setting the incorrect direction of rotation are often sources of faults resulting in production problems. • As a general rule applicable to all pumps, lengthy periods of dry running

should be avoided, as this would substantially shorten the service lives of the shaft seal, piston seal and valves. The delivery medium provides additional lubrication of those components. This principle is illustrated by the example of the floating ring seal in Fig. 3.3.

There must always be a liquid film between the contact faces of a floating ring seal.

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During inspection of the pump, checks should be made regularly while the pump is running to ensure early detection of faults, focussing in particular on the following points:

• Leakage • Noise

• Smooth running • Temperature • General condition

The reasons for pump faults are many and varied.

System-related disturbances such as pressure surges should be avoided or eliminated. Incorrectly switching system valves may stop the pumped liquid to an extreme degree, causing overlaid liquid waves to form which result in pressure surging as far as into the pump.

Trapped foreign bodies cause significant damage inside the pump. Deformed shafts, destroyed bearings and valves, as well as scraping impel-lers, are the consequences of such disturbances. Even tiny abrasive particles will cause long-term damage to the pump and the seals.

The occurrence of cavitation is a system fault which needs to be prevented. If the infeed line to the pump is incorrectly dimensioned, it is possible that a vacuum will created in the intake port, causing the medium to boil. The increase in pressure in the pump causes the boiling bubbles to implode, thereby destroying the housing and impeller.

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3.4 Checking pumps and replacing common wearing parts

In accordance with the service intervals specified in the manufacturers’ main-tenance instructions, which are additionally dependent on the specific oper-ating conditions, it is advisable to check pumps about once a year.

Bearings

The operating instructions specify that the lubricant should be changed on pumps with an enclosed gear and bearing unit.

Modern-day greased bearings are lifetime-lubricated, and merely need to be checked for smooth running.

Shaft seals

Packing glands and floating ring seals are checked for leaks and wear. Glands can be adjusted, if still possible. The gland packing should be replaced after about 2000 operating hours.

The service lives of the floating ring seals are considerably longer. They are replaced in full if worn.

Couplings

Pumps coupled to their drives by flexible couplings should be checked for flush coupling. The power-transmitting components should be checked for wear and replaced as necessary.

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. Ge rätebau, B a rsbüttel, Germany 10/2008 Pump internals

The pumps should be opened and their internals checked for wear and corrosion at the specified servicing intervals.

In the case of centrifugal pumps, as well as the shaft seal the static seal ring must be checked and replaced if worn.

The valves of reciprocating pumps, including their sealing faces, should be checked. Piston rings and packing should be checked for wear, and the plungers and sleeves checked for scoring.

Fig. 3.5 Pump unit with listed wearing part groups 20 Pump internals

Bearing Coupling Shaft seal

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3.5 Wearing parts in the pumps from the GUNT Practice Line for assembly

and maintenance

It should be stated by way of preamble that, according to the state of the art in centrifugal pumps, bearings are no longer classed as wearing parts.

MT 180 – Centrifugal pump

MT 181 – Multi-stage centrifugal pump

Fig. 3.6 Sectional drawing of the centrifugal pump

Fig. 3.7 Sectional drawing of a similar multi-stage centrifugal pump Shaft seal

(gland) Housing seal

Housing/stage seal

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. Ge rätebau, B a rsbüttel, Germany 10/2008 MT 182 – Screw pump MT 183 – Diaphragm pump

The wearing parts mentioned should be replaced during servicing.

Fig. 3.8 Exploded-view drawing of the screw pump

Fig. 3.9 Sectional drawing of the diaphragm pump

Floating ring seal Housing seal Housing seal Valves Oil filling Diaphragm Journal bearing

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. Ge rätebau, B a rsbüttel, Germany 10/2008 MT 184 – Piston pump

MT 185 – Inline centrifugal pump

Wear is to be expected on the parts marked, necessitating replacement of them.

Fig. 3.10 Drawing of the piston pump

Fig. 3.11 Exploded-view drawing of the in-line centrifugal pump

Piston seal Oil filling

Piston rod seal

Valves

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. Ge rätebau, B a rsbüttel, Germany 10/2008 MT 186 – Gear pump

Any well organised maintenance department should hold stocks of the wearing parts on the various pumps mentioned in this chapter.

Fig. 3.12 Sectional drawing of the gear pump O-rings

Floating ring seal

Housing seal Journal bearing

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. Ge rätebau, B a rsbüttel, Germany 10/2008 3.6 Shutdown

In systems in which uninterrupted running of pumps is extremely important, such as in power stations or onboard ships, replacement units are installed fully piped-up as standby units. This allows servicing or repairs to be carried out during live operation, by switching to the standby unit.

In most production environments, maintenance can only be carried out during production downtimes - that is, at partial or complete standstill. The pumps should be integrated into the system in such a way that short-interval servic-ing can be carried out without removservic-ing them. That is to say, they must be easily accessible for inspection and servicing. On the pump intake side and the delivery side stop valves should be installed.

In the case of positive-displacement pumps, the drive unit is first shut down. Immediately after the pump stops the delivery-side valve is closed, then the intake side is closed. If non-return valves are installed, they automatically act as stop valves. So installed non-return valves on the delivery side, for exam-ple, prevent possible reflux to the pump.

In the case of centrifugal pumps, the delivery-side valve is first closed, then the drive is shut down, and then the intake side is closed.

Before opening the pump, the pump and the connected piping system must be drained. This can be done either by way of sealing plugs or by carefully detaching the pipe fittings.

If the pump unit is removed completely from the system for major mainte-nance work, the safety guidelines issued by the drive manufacturers must additionally be followed.

Fig. 3.13 Installation with standby pump

Fig. 3.14 Single pump with stop valves

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. Ge rätebau, B a rsbüttel, Germany 10/2008 3.7 Repairs

Whereas during servicing parts are usually replaced following checking and as required, during repair complete wearing parts or defective components are replaced after predetermined operating cycles. These cycles are either specified by the manufacturers or they are determined by the identified condition of parts at the various maintenance intervals.

It is advisable to schedule every second to third service as a repair operation.

3.7.1 Static seals

Flat seals and O-rings used for sealing between metal components and to prevent escape of liquid from the pump body are replaced completely. Their locations include at the connection fittings and on the housing covers, floating ring seals, shaft sleeves and valves.

Procedure:

• Dismount the pump

• Remove the seals and dispose of them • Clean the parts

• Install the new seals during reassembly

• Avoid mechanical damage. Ensure cleanliness. Grease seals where necessary.

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Fig. 3.15 O-rings in a centrifugal pump Static seals

Static seals Static seal

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3.7.2 Shaft and piston rod seals

The most varied stresses on seals in pump engineering occur in the sealing of shaft and piston rod feed-throughs. These seals must act between areas subject to different pressures, and are subject to the demands of a wide variety of media, as well as having to withstand additional physical strains caused by rotating shafts or oscillating piston rods. These types of seal are known in engineering as dynamic seals. Operators expect reliable sealing, with minimal leakage, over a long service life. The shaft seals in particular should be preventively replaced during scheduled repair work, because of the extreme stresses to which they are subject.

Fig. 3.16 Example of a piston rod seal

Fig. 3.17 Example of a shaft seal

Piston rod seal

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A tried and proven method of sealing shafts is by means of soft packing glands.

This packing consists of a woven cord made principally of solid fabrics which is inserted in the packing space between the shaft and the housing, where it is deformed by an axial force and so moulded to the surfaces it is intended to seal.

To seal the pump shaft, packing glands (1) are used. These are provided in a wide range of materials and designs depending on the pump application. To protect the shaft, a shaft sleeve (2) is installed. Locking rings or ancillary glands (3) hold the packing in place. The gland press (4) compresses the packing by way of screw fittings. Correct functioning demands careful assem-bly and commissioning.

Fig. 3.18 Example of a gland Fig. 3.19 Packing gland packing 1

2 4 3

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When packing a new gland the following points need to be considered: • Correct choice of packing based on quality and dimensions

• Completely remove old packing residues (3)

• The shaft protective sleeve (7) must be free of surface damage • Insert the packing (3) with offset interfaces

• Use of sharp tools will damage the gland

• Tighten the gland press (5) by screws after inserting the packing, then slacken it slightly

• The pump shaft (2) must be loose enough to be turned slightly by hand

Fig. 3.20 Packing gland of a centrifugal pump, sectional view with zoom

Item Name

1 Washer 2 Shaft

3 Packing gland packing 4 Locking ring

5 Packing gland press 6 Stud bolt with

hexagonal nut 7 Shaft sleeve 8 Housing cover

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• Only tighten up the gland press after a run-in time of about 20-30 minutes with leakage of 50-100 drops per minute

• Adjust the gland to the required leakage rate of 3 drops per minute

To seal shaft lead-throughs which are subject to high stresses, floating ring seals are the most advantageous option nowadays. They are available in a wide range of designs, dimensions and frictional material pairings. Correctly selected, fitted and operated floating ring seals will permit longer-lasting operation of rotating positive-displacement and centrifugal pumps, with less leakage, then packing glands.

Floating ring seals are contact seals which create a yielding seal connection between stationary and rotating contact faces. Between the contact faces is a film of liquid, which assumes a stable position due to the centrifugal force occurring during rotation. The floating ring seal is sealed against the housing by means of static elastomer seals (1). The floating ring (2) rotating with the shaft is held axially in place relative to the counter-ring (4) fixed in the housing by a spring (3). The contact faces thus automatically adjust axially. Even high pressures can be controlled by means of hydraulic relief.

Fig. 3.21 Drawing of a floating ring seal

1

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Procedure for replacing the floating ring seal on a centrifugal pump shown below:

• Shut down the pump • Open the pump cover (1) • Slacken the impeller nut (2)

• Detach the impeller (3) from the shaft • Remove the floating ring (4) from the shaft

• Pull the counter-ring (5) out of the housing using a suitable implement • Assemble in the reverse order of removal

Fig. 3.22 Floating ring seal

Fig. 3.23 Example of replacing a floating ring seal on a centrifugal pump 4 1

2 3

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In view of the wide range of floating ring seal designs and pump versions, methods of removal and fitting vary. The principle illustrated here is that appli-cable to the most frequently used centrifugal pump.

The piston rod sealing in oscillating motions of the piston rods and plungers of the piston pumps is achieved by using packing glands, lipped rings, grooved rings (1) and conical rings held in support rings (2). The design and materials must always be selected to match the given operating conditions. Spring-loaded (3) seals, for example, offer uniform pre-tension, low friction and so longer service lives.

The method of removal and fitting depends on the specific pump version and design. The manufacturers’ fitting instructions are useful in this context, and should be followed.

Fig. 3.24 Drawing of a piston rod seal 1

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The same is true of the piston seals. Replacing piston rings and piston sleeves forms part of the essential scheduled repair routine. Some design variants are shown in Fig. 3.25.

Fig. 3.25 Examples of piston seals

Piston with leather/rubber sleeves

Piston with metal seal rings

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. Ge rätebau, B a rsbüttel, Germany 10/2008 3.7.3 Valves

Positive-displacement pumps such as reciprocating pumps and diaphragm pumps seal off the delivery space by means of intake and delivery side pressure valves. They open due to the resultant pressure difference on every stroke and close due to their intrinsic mass or by additional spring force. The valves of the smaller diaphragm pumps, used as metering pumps in the chemical industry, are executed as ball valves. Owing to the more precise effect achieved, twin ball valves are often installed. They are replaced by simply unscrewing the valve unit out of the housing.

The valves of the piston pumps may be executed as weight or spring-loaded disc valves.

The sealing faces are mostly metallic, and correspondingly sensitive.

After being individually removed, the discs are replaced. The valve seats are checked and re-milled or lapped as necessary. In the case of valves with an additional elastomer sealing disc, only the disc needs to be replaced, and the smooth running checked.

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3.7.4 Spare parts ordering

Maintenance work should generally be carried out on a routine basis in accordance with the maintenance instructions and safety rules laid down by the manufacturers. Key parts should be replaced at the maintenance inter-vals indicated in the operational or machine log. Arrangements should be made for parts to be procured from the supplier in advance.

Every pump has a rating plate affixed to it by the manufacturer. The rating plate indicates the manufacturer’s name, the pump model and serial number. The data is often also imprinted on the housing, so the information is still available even if the rating plate comes off. Based on this information, the exact technical and material specification can be identified.

Fig. 3.27 Examples of disc valves

Spring-loaded with flat seat and seal ring

Spring-loaded with flat seat Weighted with conical

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The details shown in Fig. 3.29 need to be quoted to the supplier when order-ing spares, so as to ensure the correct parts are supplied:

Fig. 3.28 Example of a housing with imprinted model and serial number

Fig. 3.29 Information for spare parts ordering, e.g. identified from rating plate, parts drawing or parts list

1. Pump model 2. Serial number 3. Part name

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4 Technical description of piston pump 46

4 Technical description of piston pump

4.1 Description

Piston pumps are used primarily to transport fluids at high delivery pressures and low flow rates.

At constant speed, the volumetric flow also remains constant at different pressures. A air chamber built-in to the pump damps the pressure spikes which occur on each stroke.

The pump presented here is a double-acting piston pump, which means that each stroke is simultaneously an intake and a delivery stroke.

The pump incorporates a safety valve, so that if the pressure rises too high a portion of the flow is returned to the intake side.

Typical applications of piston pumps include pumping drinking water and domestic water in residential areas, in agriculture, onboard ships and in industry and at commercial garden centres.

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. Ge rätebau, B a rsbüttel, Germany 10/2008 4.2 Mode of operation

The piston pump is driven by way of a pulley and a V-belt by an electric motor. On every revolution, the crankshaft acts by way of the connecting rod and the crosshead on the piston (1) which is mounted on the end of the piston rod. This stroke motion causes the piston to move back and forth in the cylinder bushing (2).

On every stroke the piston (1) enlarges and reduces the size of the delivery chamber. In the enlarging delivery chamber a negative pressure is created, causing the pressure valve (3) to close and liquid to flow via the intake valve (4) into the delivery chamber. In the reducing delivery chamber the piston presses the liquid via the pressure valve out of the pump body, while the intake valve is pressed closed. The piston pump investigated here has a delivery chamber on each side of the cylinder bushing. The pump is double-acting, since on every stroke it simultaneously draws in on one side and displaces on the other.

If the pressure on the delivery side (5) of the pumps is too high, the built-in safety valve (7) opens and the liquid flows inside the pump back to the intake side (6).

Fig. 4.2 Delivery principle of a double-acting piston pump

Item Name 1 Piston 2 Cylinder bushing 3 Pressure valve 4 Intake valve 1 4 3 2

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The piston pump is self-priming. It must, however, be primed prior to initial commissioning.

The pump delivery is independent of the direction of rotation of the drive. However, optimum lubrication of the gearbox can only be effected in the direction indicated by the arrow on the pump.

Fig. 4.3 Delivery principle of the piston pump

Item Name 3 Pressure valve 4 Intake valve 5 Delivery Side 6 Intake side 7 Safety valve 7 3 4 6 5

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. Ge rätebau, B a rsbüttel, Germany 10/2008 4.3 Layout

The layout of the piston pump is shown in the drawings (see chapter 9, page 209). The pump consists of the following main components:

• Air chamber with safety valve • Pump housing with valves • Piston • Gland • Crankshaft • Crosshead • Piston rod • Gearbox housing

Fig. 4.4 Component assemblies of the piston pump

2 1 4 7 6 5 8 3

Item Name Item Name

1 Air chamber with safety valve 5 Crankshaft 2 Pump housing with valves 6 Crosshead

3 Piston 7 Piston Rod

(56)

The motor is mounted on the pump unit by clamp rails.

The crankshaft, the connecting rod and the crosshead are automatically lubricated in the gearbox housing by circulating oil on every rotation.

The piston rod is sealed off from the delivery chamber by a packing gland. The sleeved piston made of NBR rubber runs in a stainless steel cylinder bushing.

The two delivery chambers each contain two disk valves with valve rubber plates.

The delivery side of the pump is executed as a air chamber, with a built-in safety valve.

4.4 Technical data

Pump model: PM 10

Power consumption: max. 0,37 kW

Max. capacity: 1000 ltr/h

Max. delivery pressure: 6 bar

Motor speed: 1450 rpm (driven by V-belt) Intake connection: 1 “ Pressure connection: 1 “ Pump materials: Pump body: GG20

Valves: Brass (CuZn39Pb3)

Cylinder bushing: X6CrNi18-10

Piston: NBR Piston rod seal: PTFE saturated packing rings

(57)

4.5 Dimensions of the piston pump

(58)

4.6 Parts drawings and parts lists

Fig. 4.6 Spare parts drawing for the piston pump

83 , 87 81 , 8 2 79 , 80 8 4 , 85 8 7 79, 80 85 , 86 8

(59)

Fig. 4.7 Spare parts drawings for the gearbox 19 6 22 21 4, 23 16 11 3 - 15 8 20 10 34 35 14 17 18 33 2 32 12 27 9 13 29 28 26 5 7 1 30,31 24 25

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Fig. 4.8 Spare parts drawings for the pump housing

42 45 63 43 40 60 51 5 0 , 52 , 53 59 39 65 47 48 61 74 62 46 , 7 7 76 75 73 72 47 67 66 58 41 54 68 69 70 71 44 57 58 38 49 37 36 64

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. Ge rätebau, B a rsbüttel, Germany 10/2008 Item Quanti ty

Unit Name Item number /

Standard

Comments

1 1 Piece Connecting rod MT184.10.04.001 2 1 Piece Packing gland housing MT184.10.05.002

3 1 Piece Crankshaft MT184.10.03.001

4 1 Piece Bearing cover, open MT184.10.10.001

5 1 Piece Gearbox housing MT184.10.09.001 EN-GJL-200 6 1 Piece Bearing cover, closed MT184.10.09.002 EN-GJL-200 7 1 Piece Gearbox cover MT184.10.09.003 DOC04 8 1 Piece Base plate MT184.10.09.004 S235JR 9 1 Piece Oil splash guard MT184.10.09.005 DOC04 10 1 Piece Packing gland seal MT184.10.09.006 SBR/B-870M 11 2 Piece Bearing cover seal MT184.10.09.007 SBR/B-870M 12 1 Piece Oil stripper MT184.10.09.008 60NBR693 SW

13 1 Piece Oil plug MT184.10.09.009 CuZn39Pb3

14 1 Piece Duo-piston PM10 Simirit

15 1 Piece Disk spring DIN 6888-5x7,5

16 8 Piece Hexagon nut ISO 4032-M6 8

18 1 Piece Spring ring DIN 127-A-8 A2

19 6 Piece Hexagon screw ISO 4017-M6x12 8.8

20 4 Piece Rubber buffer 500029 GMT

21 2 Piece Seal DIN

7603-A-10x13,5x2

PVC

22 2 Piece Angled oiler with nut G1/8 Spike 23 1 Piece Radial shaft seal DIN

3760-A-16x35x7

NBR

24 2 Piece Grooved ball bearing DIN 625-6202 25 1 Piece Grooved ball bearing DIN 625-6203 Tab. 4.1 Spare parts list

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26 1 Piece Crosshead MT184.10.04.002 EN-GJL-200 27 1 Piece Piston Rod MT184.10.04.003 X14CrMoS17 28 1 Piece Straight pin ISO 8734-12x35 C1

29 1 Piece Hexagon nut ISO 4032-M8 8-A2

30 1 Piece Hexagon screw ISO 4017-M6x25 8.8

32 1 Piece Packing gland screws MT184.10.05.002 CuZn39Pb3 33 1 Piece Brass washer MT184.10.05.003 CuZn37F30

34 1 Piece Gland packing 00.2251 Spike

35 1 Piece Lip seal ISO 4032-M8 A2-70

36 1 Piece Lock nut MT184.10.09.002 CuZn39Pb2

37 1 Piece Knurled screw MT184.10.08.003 CuZn39Pb3

38 1 Piece Cap MT184.10.08.004 NBR

39 1 Piece Pump housing MT184.10.06.001 EN-GJL-200 40 1 Piece Cylinder cover MT184.10.06.002 EN-GJL-200 41 1 Piece Air chamber MT184.10.06.003 EN-GJL-200 42 1 Piece Water plug MT184.10.06.004 CuZn39Pb2 43 1 Piece Air chamber stud bolt MT184.10.06.005 9SMn28K 44 1 Piece Cylinder pipe MT184.10.06.006 X6CrNi18-10

45 1 Piece Cap nut DIN 1587-M12 CuZn39Pb3

46 1 Piece Drain plug MT184.10.06.007 CuZn39Pb2 47 1 Piece Membrane safety valve SV.01-065.7,5

F3000.4

Spike

48 2 Piece Straight flange G1“ MT184.10.06.010 EN-GJL-200 49 1 Piece Poppet valve body MT184.10.08.001

50 2 Piece Valve bridge MT184.10.06.008 X14CrMoS17 51 1 Piece Cylinder cover seal MT184.10.06.009 SBR/B-870M

Item Quanti ty

Standard

Comments

(63)

52 2 Piece Flat washer ISO 7089 -8 8-A2

54 1 Piece Air chamber seal MT184.10.06.011 SBR/B-870M

55 2 Piece Seal DIN

7603-A-10x13,5x2

PVC

56 2 Piece Stud bolt MT184.10.06.012 X17CrNi16-2 57 2 Piece Stud bolt MT184.10.06.013 X17CrNi16-2

58 2 Piece Seal DIN

7603-A-13x18x1,5

PVC

59 4 Piece Valve seat seal MT184.10.06.014 SBR/B-870M 60 3 Piece Hexagon screw ISO 4017-M6x16 8.8-A2 61 3 Piece Hexagon screw ISO 4017-M8x25 8.8-A2

62 2 Piece Seal MT184.10.06.015 SBR/B-870M

63 1 Piece Plain washer MT184.10.06.016 X17CrNi16-2

64 1 Piece Seal DIN

7603-A-13x18x1,5

PVC

65 1 Piece Seal DIN

7603-A-39x49x2

EPDM

66 1 Piece Valve seat MT184.10.07.001 CuZn40Al2 67 1 Piece Seal in valve seat MT184.10.07.002 80 NBR 180 68 1 Piece Delivery side valve pin MT184.10.01.001 CuZn39Pb3 69 1 Piece Delivery side valve seat Mt184.10.01.002 CuZn39Pb3 70 1 Piece Valve rubber plate MT184.10.01.003 NBR-45°

Shore A 71 1 Piece Hold-down MT184.10.01.004 CuZn39Pb3 72 1 Piece Intake side valve pin MT184.10.02.001 CuZn39Pb3 73 1 Piece Intake side valve seat MT184.10.02.002 CuZn39Pb3 74 1 Piece Valve rubber plate MT184.10.01.003 NBR-45°

Shore A

Standard

Comments

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75 1 Piece Hold-down MT184.10.01.004 CuZn39Pb3

76 1 Piece Hexagon nut ISO 10511.M6 A2

77 1 Piece Drain plug MT184.10.06.007 CuZn39Pb2 78 1 Piece Rocker shaft MT184.10.00.001 X14CrMoS17 79 1 Piece Rocker shaft with thread MT184.10.00.002 X14CrMoS17 80 4 Piece Insulating bush MT184.10.00.003 GP-22 81 1 Piece Motor clamp rail left MT184.10.00.004 EN-GJL-200 82 1 Piece Motor clamp rail right MT184.10.00.005 EN-GJL-200 83 1 Piece V-belt pulley MT184.10.00.006 EN-GJL-200 84 1 Piece Hexagon screw ISO 4017-M8x25 8.8

86 2 Piece Flat washer ISO 7089-A-8 140 HV

87 3 Piece Hexagon screw ISO 4017-M6x-10 8.8 88 1 Piece Valve housing complete MT184.00.06.000 89 1 Piece Crankcase complete MT184.00.09.000 90 1 Piece Intake valve complete MT184.00.01.000 91 1 Piece Pressure valve complete MT184.00.02.000

92 1 Piece Valve seat MT184.00.07.000

Standard

Comments

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5 Assembly and dismantling of the piston pump 59

5 Assembly and dismantling of the piston pump

5.1 Assembly of the piston pump

The piston pump assembly procedure is divided into eight phases: • Assembly phase 1 – Crankshaft (assembly unit 1)

• Assembly phase 2 – Connecting rod with piston rod (assembly unit 2) • Assembly phase 3 – Packing gland (assembly unit 3)

• Assembly phase 4 – Intake valve (assembly unit 4) • Assembly phase 5 – Pressure valve (assembly unit 5) • Assembly phase 6 – Gearbox (assembly unit 6) • Assembly phase 7 – Pump housing (assembly unit 7) • Assembly phase 8 – Pump

Tools: • Puller • Punch

• Wrench size 10 (2 x), size 13, size 14, size 19 and size 22 • Screwdriver

• Vice – not supplied • Soft hammer • Jig 1, 2, 3 and 4

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5.1.1 Assembly phase 1 – Crankshaft (assembly unit 1)

Fig. 5.1 Drawing of the crankshaft (assembly unit 1)

Fig. 5.2 Crankshaft, fully assembled (assembly unit 1)

Item Name

3 Crankshaft

24 Grooved ball bearing 25 Grooved ball bearing

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Fig. 5.3 Parts required for assembly

Item Name

3 Crankshaft

24 Grooved ball bearing 25 Grooved ball bearing

(68)

Procedure for assembling the crankshaft (assembly unit 1)

Grooved ball bearing (item 25)

Grooved ball bearing (item 24) Crankshaft

(item 3)

Crankshaft (assembly unit 1)

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Assembly procedure for crankshaft (assembly unit 1)

• Lightly oil crankshaft (3) to aid assembly of grooved ball bearings.

• Fit grooved ball bearing (25) onto crankshaft (3) and position at connecting rod seat.

• Using a soft hammer and jig 2, drive grooved ball bearing (25) onto crankshaft, without bending it, until grooved ball bearing contacts recess.

• Fit grooved ball bearing (25) onto drive side of crankshaft (3).

(70)

(71)

5.1.2 Assembly phase 2 – Connecting rod with piston rod (assembly unit 2)

Fig. 5.6 Drawing of connecting rod with piston rod (assembly unit 2)

Fig. 5.7 Connecting rod with piston rod, fully assembled (assembly unit 2)

1 Connecting rod 29 Hexagon nut 26 Crosshead 30 Hexagon screw 27 Piston Rod 31 Hexagon nut 28 Straight pin

(72)

1 Connecting rod 29 Hexagon nut 26 Crosshead 30 Hexagon screw 27 Piston Rod 31 Hexagon nut 28 Straight pin

29 26 28 31 30

27

(73)

Procedure for assembling the connecting rod with piston rod (assembly unit 2) Crosshead (item 26) Straight pin (item 28) Hexagon nut (item 29) Connecting rod (item 1)

Connecting rod with piston rod (assembly unit 2)

Piston rod (item 27)

Hexagon screw with hexagon nut

(74)

Assembly procedure for connecting rod with piston rod (assembly unit 2)

• Fit crosshead (26) onto connecting rod (1).

• Using a soft hammer and punch, carefully drive straight pin (28) into hole in crosshead (26) and connecting rod (1).

• Screw hexagon nut (29) onto thread of piston rod (27).

• Screw piston rod with thread side onto which nut was screwed into crosshead.

• Tighten hexagon nut against crosshead.

• Screw hexagon screw with hexagon nut (30, 31) into end of connecting rod.

(75)

5.1.3 Assembly phase 3 – Packing gland (assembly unit 3)

Fig. 5.10 Drawing of the packing gland (assembly unit 3)

Fig. 5.11 Packing gland, fully assembled (assembly unit 3)

Item Name

2 Packing gland housing 32 Packing gland screw 33 Brass washer 34 Gland packing 35 Lip seal 35 32 33 2 34

(76)

Fig. 5.12 Parts required for assembly 32

33

2, 35

34

Item Name

2 Packing gland housing 32 Packing gland screw 33 Brass washer 34 Gland packing 35 Lip seal

(77)

Procedure for assembling the packing gland (assembly unit 3)

Brass washer (item 33)

Packing gland packing (item 34) Packing gland housing

with lip seal (item 2, 35)

Packing gland (assembly unit 3)

Packing gland screw (item 32)

(78)

Assembly procedure for packing gland (assembly unit 3)

NOTICE

The lip seal (35) is not suitable for repeated assembly and disassembly, as it would be damaged. It is pre-assembled.

• Insert brass washer (33) into packing gland housing (2).

• Push four packing gland packs (34) into packing gland housing (2). The abutment of each must be at a 90° offset.

• Screw packing gland screw (32) into packing gland housing.

(79)

5.1.4 Assembly phase 4 – Intake valve (assembly unit 4)

Fig. 5.14 Drawing of the intake valve (assembly unit 4)

Fig. 5.15 Intake valve, fully assembled (assembly unit 4)

Item Name

72 Intake side valve pin 73 Intake side valve seat 74 Valve rubber plate 75 Hold-down 76 Hexagon nut 72 73 74 75 76

(80)

Item Name

72 Intake side valve pin 73 Intake side valve seat 74 Valve rubber plate 75 Hold-down 76 Hexagon nut

76 75

(81)

Procedure for assembling the intake valve (assembly unit 4)

Valve rubber plate (item 74)

Hold-down (item 75)

Intake side valve pin with intake side valve seat

(item 72, 73)

Intake valve (assembly unit 4)

Hexagon screw (item 76)

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Assembly procedure for intake valve (assembly unit 4)

NOTICE

The intake side valve pin (72) is pre-assembled with the intake side valve seat (73).

• Fit valve rubber plate (74) onto intake side valve pin (72) with curved side facing outwards.

• Fit hold-down (75) onto valve pin with cylindrical side first.

• Screw hexagon nut (76) onto valve pin.

• Carry out same assembly procedure for second intake valve.

(83)

5.1.5 Assembly phase 5 – Pressure valve (assembly unit 5)

Fig. 5.18 Drawing of the pressure valve (assembly unit 5)

Fig. 5.19 Pressure valve, fully assembled (assembly unit 5)

Item Name

68 Delivery side valve pin 69 Delivery side valve seat 70 Valve rubber plate 71 Hold-down 68

71 70 69

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Item Name

68 Delivery side valve pin 69 Delivery side valve seat 70 Valve rubber plate 71 Hold-down

71 68

MT184CP

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