Lift check valves

Nominal valve size Gate Globe, lift check, swing check A and B Angle and lift check B... 

For the standby pump start test, which is an important test to ensure the pumps transfer without large pressure swings, a check should be made to see if the relief valves lift or the pressure falls to a pressure one half the difference between the standby pump start pressure and the compressor trip pressure. The transient pressure is best measured with a multipen chart recorder. The chart speed must be high enough to fully display the pressure variation. While not as good as the chart recorder, a simple shop-made test setup can be substituted. A spare switch is temporarily connected to the same location as the other switches. This switch is calibrated to close at the threshold acceptance pressure. The contacts are wired to a test light through a seal relay. The purpose of the relay is to maintain the cir-... 

Figure 15-11. Lift check valve. [Courtesy of Jenkins Bros.)...

A continuous flow reactor vessel contains a liquid reacting mixture with a density of 0.85 g/cm3 and a viscosity of 7 cP at 1 atm pressure. Near the bottom of the vessel is a I i n. outlet line containing a safety relief valve. There is 4 ft of pipe with two 90° elbows between the tank and the valve. The relief valve is a spring-loaded lift check valve, which opens when the pressure on the upstream... 

An oil with a 32.6° API gravity at 60°F is to be transferred from a storage tank to a process unit that is 10 ft above the tank, at a rate of 200 gpm. The piping system contains 200 ft of 3 in. sch 40 pipe, 25 90° screwed elbows, six stub-in tees used as elbows, two lift check valves, and four standard globe valves. From the pump performance curves in Appendix H, select the best pump to do this job. Specify the pump size, motor speed, impeller diameter, operating head and efficiency and the horsepower of the motor required to drive the pump. 

Lift Check Valves These valves (Figs. 10-160 through 10-162) are made in three styles. Vertical lift check valves are for installation in vertical lines with flow normally upward. Globe (or piston) valves with a 90° bonnet (Fig. 10-161) are for installation in horizontal lines, although inclined bonnet versions (approximately 45°) with spring... 

Check valves (o) lift check (i>) ball check (c) swing check. 

Lift-check and swing-check are the two major value types of valves used in process work. The lift-check, or ball-check, is most often used in two-inch and smaller sizes. It has a ball or guided plug which is lifted by fluid pressure and does not have a tendency to slam — as the swing-check type does. For this reason, the lift-check valve is preferable for services having irregular or frequent reversals of flow. 

Stop check, which combines design characteristics of both a lift check and a globe valve. In the closed position, the stop check disc is firmly seated. In the open position, the stem rises out of the body of the flow control element and acts like a guide for the disc. In the open position, the stop check valve functions like a lift check valve with one exception The degree of lift can be controlled. 

Lift Check Valve. A lift check valve is similar in design to a globe valve except that the disk is Ufted by the forward line pressure and closed by gravity and backflow (Fig. 5.185). 

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