Some of the most common types of valves are:
17.1 GATE VALVES
Best suited control: Quick opening Recommended uses:
1. Fully open/closed, non-throttling 2. Infrequent operation
3. Minimal fluid trapping in line
Applications: Oil, gas, air, slurries, heavy liquids, steam, non-condensing gases, and corrosive liquids
Advantages Disadvantages High Capacity Poor control
Tight shut-off Cavitate at low pressure drops Low cost Cannot be used for throttling Little resistance to flow
17.2 GLOBE VALVES
Best suited control: Linear and equal percentage Recommended uses:
1. Throttling service/flow regulation 2. Frequent operation
Applications: Liquids, vapors, gases, corrosive substances, slurries
Advantages Disadvantages Efficient throttling High pressure drop
Accurate flow control More expensive than other valves Available in multiple ports
17.3 BALL VALVES
Best suited control: Quick opening, linear Recommended uses:
1. Fully open/closed, limited-throttling 2. Higher temperature fluids
Applications: Most liquids, high temperatures, slurries
Advantages Disadvantages High Capacity Poor control
Tight sealing with low torque Prone to Cavitation Low cost
Low leakage and maintenance
17.4 BUTTERFLY VALVES
Best suited control: Linear, equal percentage Recommended uses:
1. Fully open/closed or throttling services 2. Frequent operation
3. Minimal fluid trapping in line
Applications: Liquids, gases, slurries, liquids with suspended solids
Advantages Disadvantages High Capacity High torque required for control
Good flow control Prone to Cavitation at lower flows Low cost and maintenance
Low pressure drop
17.5 OTHER VALVES
1) Another type of valve commonly used in conjunction with other valves is called a check valve. Check valves are designed to restrict the flow to one direction. If the flow reverses direction, the check valve closes.
2) Relief valves are used to regulate the operating pressure of incompressible flow.
3) Safety valves are used to release excess pressure in gases or compressible fluids.
17.6 CONTROL VALVES
Control valves are of three types based on how the valve travel or stroke (openness) relates to the flow:
• Equal Percentage: equal increments of valve travel produce an equal percentage in flow change
• Linear: valve travel is directly proportional to the valve stoke
• Quick opening: large increase in flow with a small change in valve stroke 17.7 SOME RULES OF THUMB
Equal Percentage (most commonly used valve control)
• Used in processes where large changes in pressure drop are expected
• Used in processes where a small percentage of the total pressure drop is permitted by the valve
• Used in temperature and pressure control loops Linear
• Used in liquid level or flow loops
• Used in systems where the pressure drop across the valve is expected to remain fairly constant (i.e. steady state systems)
Quick Opening
• Used for frequent on-off service
• Used for processes where "instantly" large flow is needed (ie. safety systems or cooling water systems)
17.8 CONTROL VALVE FLOW COEFFICIENT
17.8.1 CV FOR INCOMPRESSIBLE FLUID
The limiting pressure drop corresponding to the occurrence of the critical flow is defined as:
∆Pcritical =P1−Pv
Control valve flow coefficient can be calculated using the following formulas:
VC
Where P1 = Upstream pressure (bara) P2 = Downstream pressure (bara)
Pv = Vapor pressure of liquid at flowing temperature (bara) Pc = Critical pressure of liquid (bara)
Pvc = Differential pressure between the inlet pressure and the pressure at Vena Contracta (bar)
T = Upstream flowing temperature (K) G = Specific gravity @STP
Cf = Pressure recovery factor (assume 0.8 – 0.9 if no data is available) Cv = Valve flow coefficient
Q = Volumetric flow rate (m³/h) @STP
17.8.2 CV FOR COMPRESSIBLE FLUID
The limiting pressure drop corresponding to the occurrence of the critical flow is defined as:
∆Pcritical =0.5⋅Cf2⋅P1
Control valve flow coefficient can be calculated using the following formulas:
STP
NORMAL FLOW
Where P1 = Upstream pressure (bara) P2 = Downstream pressure (bara) T = Upstream flowing temperature (K) Ts = Steam superheat temperature (°C) G = Gas specific gravity @STP
Cf = Pressure recovery factor (assume 0.8 – 0.9 if no data is available) Cv = Valve flow coefficient
W = Mass flow rate (tph)
Q = Volumetric flow rate (m³/h) @STP
17.9 CONTROL VALVE ISOLATION AND BYPASS VALVE SIZE
Control Valve Size Dia. Block
& By-pass
Valve Size ½” ¾” 1” 1½” 2” 3’ 4” 6” 8” 10” 12” 14” 16”
Φ = ½” ½”
Φ = ¾” ¾” ¾”
Φ = 1” 1” 1” 1’
Φ = 1½” 1½” 1½” 1½” 1½”
Φ = 2” 2” 2” 2” 2”
Φ = 3” 2” 2” 3” 3”
Φ = 4” 3” 3” 4” 4”
Φ = 6” 4” 4” 6” 6”
Φ = 8” 6” 6” 8” 8”
Φ = 10” 8” 8” 10” 10”
Φ = 12” 10” 10” 12” 12”
Φ = 14” 12” 14” 14”
Φ = 16” 12” 14” 16”
CONTROL VALVE MANIFOLD
D 3/4"
1) For control valve diameter < 4" in continuous service, complete manifold (block+bypass) shall be provided
2) For control valve diameter > 4" the need for installation of block & bypass valve and handwheel around the control valve shall be defined for case by case 3) Bypass valves are globe valves for size <8" or butterfly valves for size >6"
D 3/4"
IF REQUIRED
17.10 POSITIVE ISOLATION OF EQUIPMENT
All equipment with spare, by-pass or inspectable are isolated by spacer or spectacle blinds for allowing safe maintenance in the following cases:
• Hydrocarbon service
• Chemical product (operating pressure ≥ 75 barg)
• Other service for operating temperature T ≥ 170°C
Drums (in all cases), columns, filters and all pressure vessels will be isolated for maintenance.
The used of spectacle blind or spacer will be in accordance with the following table:
150# Φ ≤ 4” Φ ≥ 6”
300# Φ ≤ 3” Φ ≥ 4”
600# Φ ≤ 1½” Φ ≥ 2”
900# Φ ≤ 1½” Φ ≥ 2”
1500# Φ ≤ 1½” Φ ≥ 2”
2500# Φ ≤ 1½” Φ ≥ 2”
DOUBLE VALVING ARRANGEMENT
D 3/4"
D 3/4" 3/4"
3/4"
D
D TRAIN A
TRAIN B COULD BE SDV
1) Double valving will be provided if the operating pressure is higher or equal than 75 barg and for piping rating > 600#
2) Type of valve and isolation by spacer or spectacle blind must be as per the standard practice
17.11 TYPE OF ISOLATION VALVE ACCORDING TO SERVICE
Hydrocarbon Liquid/Gas Chemical Product, Air,
Nitrogen, Inert gas & CO2 Glycol Sea Water, Cooling Water &
Hot Water
Φ ≤ 2” → Ball valve FB( ) Φ ≤ 2” → Ball valve FB(
)
Same criteria as hydrocarbon services if operating temperature is ≥ 170 oC, the type of ball valve will be revised.
Pressure valve to flare:
→ Ball valve FB ( ) be used for the other cases.
Also SDV (except if located at equipment suction).
Reduced ball valve ( ) will be used for the other cases. Also SDV (except if located at equipment suction).
The process will decide if ( ) is acceptable or not for the different services.
The process will decide if ( ) is acceptable or not for the different services.
INJECTION WATER
Limit of ball valve utilization:
T = 170 oC
If operating temperature is ≥ 170°C, the type of ball valve will be revised.
Limit of ball valve utilization:
T = 170 oC
If operating temp. is ≥ 170°C, the type of ball valve will be revised.
P > 150 bar → Ball valve ( )
17.12 TYPCAL VALVE ARRANGEMENTS
PRESSURISATION BY-PASS
DO 3/4"
1/2"
2"
DETAILS OF SAMPLE CONNECTION
SP AS IN PID DRAWING
Liquid sample connection with temperature < 65°C and a vapor pressure < ATM
Process or Utility class UTILITY INJECTION Injection dia > 3/4"
PROCESS LINE
600 min SPEC BREAK
LO
1) Distance between PSV and reducer is minimum
2) Downstream block valve is installed flange to flange (if the builtup back pressure is high this valve is installed downstream the reducer)
3) The minimum distance of 600 mm is required in case of cold depressurisation to avoid icing of the ball valve
NUMBER OF PSV & SET PRESSURE
1) Only one PSV is installed for Thermal or Fire relief case
2) 1+1 or multiple PSVs are installed for other relief cases. The total relief load is shared by all the operating PSVs
3) For multiple PSVs one PSV is set at Design pressure and is in operation while a similar PSV is in standby. All other PSVs are set at 105% of set pressure and are in operation.
PUMPS HANDLING HYDROCARBON & GLYCOL
3/4"
3/4"
3/4"
3/4"
3/4"
COLLECTED DRAIN UC
UC NOTES:
1) "Y" type strainer are installed for lines <6"
and "T" type strained are installed for lines >4"
2) For water services the pump drains are collected in a tray which is routed to open drain 3) A bypass around the pump non-return valve shall be installed if the pump operating temp is
>80°C for spare pump heating or for draining the spare pump discharge side
4) Utility connection (UC) is required only for hydrocarbon services
DRAINAGE PIPING FROM HORIZONTAL VESSELS
COLLECTED DRAIN
D 3/4"
SPEC BREAK Level instr. drain
2"
DRAINAGE PIPING FROM VERTICAL VESSELS AND PROCESS PIPING
COLLECTED DRAIN
SPEC BREAK Level instr. drain
D 3/4"
2"
PROCESS LINE