MECHANICAL SEAL

The drive and non-drive end stuffing boxes are fitted with mechanical seals mounted on seal sleeves and located within seal cooling jackets to prevent feed water escaping along the shaft. Tapped holes are provided on each seal plate and cooling jacket for clarified cooling water inlet and outlet connections.

3.7 Journal and Thrust Bearings

The rotating assembly is supported at each of the shaft by a white metal lined journal bearing and the residual thrust is carried by a titling pad double thrust bearing mounted at the non-drive end of the pump.

The journal bearing shells are of mild steel, white metal lined, thick wall type and are split on the horizontal plane through the shaft axis. Each bearing is secured in a bearing housing and prevented from rotating by a dowel pin located in the bearing keep.

The thrust bearing has eight white metal lined titling pads held in a split carrier ring positioned on each side of the thrust collar. The carrier rings are prevented from rotating with the shaft by dowel pins in each ring which engage in slots in the bearing housing top half. The thrust pads are retained on the carrier rings by a special pad stops screwed into the rings.

A split floating oil sealing ring is located in a groove in the thrust bearing housing to restrict the escape of lubricating oil from the thrust bearing chamber. To ensure that the thrust bearing remains flooded, an orifice is fitted at the oil outlet.

Machined spacers are fitted behind the carrier rings to effect the axial position setting of the rotating assembly on the original build. The bearings are supplied with lubricating oil from the forced lubrication oil system.

3.8 Bearing Housings

The bearing housings are in the form of cylindrical castings split on the horizontal shaft axis. The top and bottom halves, of each bearing housing, are located by fitted bolts and secured together by cap screws. The journal bearing in each housing is located by a dowel pin in the bearing keep and the bearing keep is dowel located to the bottom half housing and secured by cap screws. On the top half housing there is provision for an air vent, vibration probes and a temperature check point. On the bottom half housing there is provision for oil inlet and oil outlet, R.T.D. probe and a temperature gauge.

The drive end bearing housing is secured to the suction guide by cap screws and is radially located by dowel pins fitted in the flange of the suction guide. Oil guards fitted in a groove at each end of the bearing housing are dowel located and serve to prevent oil escaping from the housing.

An air breather is screwed into a tapped hole in the top half bearing housing and a tapped hole is provided for a temperature gauge. Connections for an oil inlet and an oil outlet are provided in the bottom half bearing housing.

The non-drive end bearing housing, which contains both the journal and thrust bearings, is located by taper dowel pins and secured to the gland housing by cap screws. In addition to the features common to both bearing housings the follow features are included. On the top half housing there are connections for reverse running indicators, an accelerometer and a thrust bearing temperature check point. On the bottom half bearing housing the additional provision is for thrust bearing temperature gauges. Leakage of lubricating oil from the non-drive end bearing housing is prevented by an oil guard in the inboard side of the housing.

3.9 Hydraulic Balance :

The rotating assembly is subject to varying forces due to the differential pressure forces acting on the impellers. The pump has therefore been designed so that the shaft is kept in tension by the location of a balance drum at the non-drive end, and is hydraulically balanced so that only a small residual thrust remains, which is carried by the thrust bearing. The main components of the hydraulic balancing arrangement are the balance chamber machined in the discharge cover, the balance drum which is secured to the shaft and the balance drum bush fitted in the bore of the discharge cover. The thrust caused by the discharge pressure acting on the area outside each impeller wear ring on the inlet side of the impeller wear ring is balanced by the same pressure acting on an equal area on the outlet side of each impeller. The thrust caused by the suction pressure acting on the area inside the wear ring on the inlet side of each impeller is overcome by the much greater thrust caused by the discharge pressure acting on an equivalent area on the outlet side of each impeller. The resultant thrust force, due to the different pressures acting on these equal areas, tends to move the rotating assembly towards the drive end of the pump.

The thrust force will vary with the load on the pump but the hydraulic balance arrangement will reduce its effect, enabling the residual thrust to be taken by the titling pad thrust bearing. This bearing has a double face so that the surges in opposite directions which occur during the start-up period and during transient conditions will be accommodated.

The hydraulic balance arrangement operates as follows:-

The pump product passes from the kicker stage of the pump between the balance drum and the bush, and enters the balance chamber at a pressure approximately equal to the suction pressure. Two ports in the discharge cover allow the product to be piped back to the pump suction side. The pressure differential across the balance drum is therefore equal to the across the impellers.

The cross-sectional area of the balance drum is sized to give a small residual thrust towards the drive end of the pump.

SECTION - B

BOILER FEED PUMP

CHAPTER - 2

OPERATING INSTRUCTIONS

LIST OF CONTENTS

1. Introduction 2. Preparation for starting 3. Start – up

4. Routine checks

5. Trip condition

6. Shut-down 7. Stand by conditions

8. Fault finding

CHAPTER – 2

OPERATING INSTRUCTIONS