Suction valve

Figure 10-48 is a direc t-acting pump, designed for use at pressures up to 0.690 MPa (100 Ibfiin"). In this figure, the piston consists of disks A and B, with packing rings C between them. A bronze liner for the water cyhnder is shown at D. Suction valves are Ei and Eo. Discharge valves are Fi and Fo. 

According to the Standards of the Hydraulic Institute, a suction lift test is performed on the pump and the pressure in the suction vessel is lowered to the point where the pump suffers a 3% loss in total head. This point is called the NPSHr of the pump. Some pump manufacturers perform a similar test by closing a suction valve on a test pump and other manufacturers lower the suction elevation. 

Hf system valves = Hf suction valves + Hf discharge valves... 

The pressure upstream of the suction valve will increase until sufficient back-pressure is established on the wells or equipment feeding the compressor to reduce the flow to a new rate in equilibrium with that being handled by the cylinder or until a flare valve or relief valve is actuated. 

Suction throttle valves are common in gas-lift service to minimi/c the action of the flare valve. Flow from gas-lift wells decreases with increased back-pressure. If there were no suction valve, the flare valve may have to be set at a low pressure to protect the compressor. With a suction valve it may be possible to set the flare valve at a much higher pressure slightly below the working pressure of the low-pressure separator. The difference between the suction valve set pressure and the flare valve set pressure provides a surge volume for gas and helps even the flow to the compressor. 

As the piston starts its suction stroke, the gas that remains in the cylinder in the fixed and added clearance areas expands until the pressure in the cylinder is equal to the pressure in the line outside of the cylinder. The greater the clearance, the longer it takes for the suction valves to open and the less new gas enters the cylinder. Therefore, less gas will be compressed as cylinder clearance is increased. 

A pump was being dismantled for repair. When the cover was removed, hot oil, above its auto-ignition temperature, came out and caught fire. Three men were killed, and the plant was destroyed. Examination of the wreckage after the fire showed that the pump suction valve v/as open and the drain valve shut [3]. 

The pump had been awaiting repair for several days when a permit-to-work was issued at 8 a.m. on the day of the fire. The foreman who issued the permit should have checked ahead of time that the pump suction and delivery valves were shut and the drain valve open. He claimed that he did so. Either his recollection was incorrect or, after he inspected the valves and before work started, someone closed the drain valve and opened the suction valve. When the valves were closed, there was no indication—on them—of why they were closed. An operator might have opened the suction valve and shut the drain valve so that the pump could be put on line quickly if required. 

Although the indicated temperature had risen, the temperature of the reactor s contents had not. Pump J2, running with a closed suction valve, got hot, and the heat affected the temperature point, which was close to the pump. 

The explosion was due to a failure to directly measure the property that we wish to know. The temperature point was not measuring the temperature in the reactor but the temperature near the pump. This got hot because the pump was running with a closed suction valve. Similarly, the trip initiator on J2 showed that its motor was energized. It did not prove that there was a flow. 

SUCTION VALVES—AREA EACH, SQ. IN.-DISCHARGE VALVES—NUMBER------... 

Condition 4 Figure 12-12. Start of gas suction into cylinder. The cylinder pressure has dropped below the system suction pressure, and the suction valve opens to admit new gas into the cylinder as it returns to condition (1). 

Figure 12-11. Ideal pressure-volume cylinder action for single-acting compressor cylinder with related piston positions. Note DV = discharge valve SV = suction valve k or n may be exponent for gas. (Used and adapted by permission Gas Engineers Handbook, 1= Ed., 1977. Industrial Press, Inc.,New York. All rights reserved.)...

This is the total volume remaining in the cylinder at the end of the piston stroke. This consists of the volume between the end of the piston and the cylinder head, in the valve ports and the volume in the suction valve guards and the discharge valve seats. See Figures 12-12,12-17A, and 12-17B. 

Capacity can be accomplished in several ways as illustrated in Figures 12-28-12-31A. In Figure 12-31 (A) suction valve... 

Clearance Pocket Open) (Suction Valves Held (Suction Valves Held... 

Capacity (Suction Valves Held Open Both Ends)... 

Figure 12-31. Capacity control suction valve unloaders are available in either of two designs with pneumatic operators (A) direct-acting (air to unload) (B) reverse-acting or fail safe (air to load), which automatically unloads the compressor in the event of control air failure (C) an innovation in manually operated unloaders. Here, the lever cam arrangement provides positive loading or unloading, eliminating the requirement to turn a handwheel completely in or out. (Used by permission Bui. 9-201B, 1991. Cooper-Cameron Corporation.)...

Incomplete filling of the cylinders can result in hammering, which produces destructive pressure peaks and shortens the pump life. Filling problems become more important with higher piston velocities. The suction pressure loss through the suction valve and seat is from 5 to 10 psi. Approximately 1.5 psi of pressure is required for each foot of suction lift. Since the maximum available atmospheric pressure is 14.7 psi (sea level), suction pits placed below the pump should be... 

A few strokes of the piston in a dry liner may ruin the liner. When the pump does not fill by gravity or when the cylinders have been emptied by standing too long or by replacement of the piston and liner, it is essential to prime the pump through the suction valve cap openings. 

Air reservoirs are designed to receive and store pressurized air. Pressure regulating devices are installed to maintain the pressure within operational limits. When the air reservoir is pressurized to the maximum pressure set-point, the pressure regulator causes the air compressor to off-load compression by initiating an electrical solenoid valve to use lubricating oil to hydraulically hold open the low pressure suction valve on the compressor. 

As the compressed air is used, the pressure drops in the reservoir until the low-pressure set point is reached. At this point, the pressure regulated solenoid valve is deenergized. This causes the hydraulic force to drop off on the low-pressure suction valve, restoring it to the full compression cycle. 

An alternative valve design uses a conical discharge valve in the centre of the cylinder head, with a ring plate suction valve surrounding it. This construction is used in compressor bores up to 75 mm. 

The construction of multicylinder machines gives the opportunity to change the working swept volume by taking cylinders out of service with valve-lifting mechanisms. The ring plate suction valve which is located at the crown of a loose liner can be lifted by various... 

Figure 4.9 Lifting mechanism for ring plate suction valve (Courtesy of APV Baker Ltd (Hall Division)...

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