The control valve is a device that is created or designed specifically to direct, start, stop, mix,
The control valve is a device that is created or designed specifically to direct, start, stop, mix, or regulate the temperature, flow, or pressure of a process fluid. Mostly the control valve is manufactured by using certain materials like steel, iron, plastic, brass, bronze, etc. So in order to check the ability or quality of the valve we need to do the valve testing. So we should test the valve before it is used in the system, the test would assure that the valve would work properly. Manufacturers do certain tests on control valves in order to check their quality.
Types of valve test
Operating test
In this test, each valve will be operated more than once and this test will be conducted in a way that we could determine if these valves are suitable for the applications for which it is designed for. In this test, we can determine if all the parts of the valve are functioning properly or not. If the valve is not functioning according to the standard then it must be rejected. The faults in the valve must be cleared and the test should be conducted again till the valve perform properly in the application for which it is designed for.
Shell test
In this test, the valve will be in the open position and a hydrostatic test pressure will be applied to the valve which will be twice its rated working pressure. So during this process, there shouldn’t be any leakage through the metal, joints, or the stem steals. This test is conducted to determine the ability of the valve during critical conditions. We can determine if the valve leaks or not by doing this test. So in order to do the test, the valve should be mounted on the test bench and the valve body will be subjected to the hydrostatic test. The pressure must not be dropped while conducting the test.
Shell test procedure
Seat test
In this type of test, the test will be done from all the direction and this test will be conducted according to the operating pressure of the valve. This test is conducted to determine the sealing ability of the valve from both the flow direction. There shouldn’t be any leakage from the metal, or through the seats. The check valve seats are tested in the stopped-flow direction.
Seat test procedure
In the seat test for the globe and gate valves it would be done in the normal flow direction of the valve. In the check valves these tests will be conducted in the reverse flow direction of the valve. The seat test can be done in preferred direction for the ball and butterfly valve.
Torque test
In this test, the valve will be torqued in both the open and closed positions to make sure that there is no stem or seating damage or a seal failure. The amount of torque that will be used for this test will be related to the valve standard.
Gland test
The hydrostatic test is a combination of shell test and gland test. The gland test is conducted to detect the leakage in the actuator part. In order to check the gland leak in the air to close the control valve, the flange will be fitted on both sides of the control valve body and the air supply is removed and water will be supplied. In the air to open control valve this test will be conducted by fitting the flange on both sides of the body with air pressure and a certain amount of water pressure will be applied and this will be according to the valve standard.
Backseat test
This test should be done for most of the valves and this test is not needed for the bellow seal valve because these valves have the backseat feature. We can do this on those valves by applying the pressure inside the assembled valve with the valve end closed, the valve fully open. If the back seat test is going to be conducted after the shell test then the packing must be installed and we must retighten the packing glands after the backseat test.
Low pressure closure test
This test must be conducted by cleaning the sealing surface and it must be clean from oil, Greece, and sealant.
High pressure closure test
This test is the same as the low-pressure closure test and the only difference is that, during the liquid test, leakage should be detected when drops and not bubbles.
Special tests
Fire-test & Antistatic device testing
These tests are special tests and they must be done according to the manufacturer’s agreed procedure.
The valves which are designed to permit the emergency sealant to the seating area must be tested with the injection system empty. If we use the liquid as a test medium then the valve should not have any trapped air. A protective coating is needed such as paint which could mask the surface defects. During the closure testing of the valve, we must not use excessive pressure to close the valve.
We must choose air, kerosene, inert gas, or water for the shell test, seat test, and also for high-pressure closure test. We should use inert gas or air for the low-pressure closure or for the low-pressure back seat test. When water is used for any test then there should be a water-soluble oil or rust inhibitor.
The valve leakage can be checked by using a hydrostatic test liquid or a pneumatic test gas. It’s not possible to get zero leakage