Various valve pressure testing methods – a valuable resource!

Generally, industrial valves do not undergo strength tests during use. However, strength tests should be performed on valve bodies and covers that have been repaired or have suffered corrosion damage. For safety valves, their set pressure, reseating pressure, and other tests should comply with their instruction manuals and relevant regulations. Strength and sealing tests should be performed on valves before installation. 20% of low-pressure valves should be randomly inspected; if any fail, 100% should be inspected. Medium and high-pressure valves should be 100% inspected. Commonly used media for valve pressure testing include water, oil, air, steam, and nitrogen. The pressure testing methods for various industrial valves, including pneumatic valves, are as follows:

 

1. Pressure Testing Method for Ball Valves

 

The strength test of a pneumatic ball valve should be conducted with the ball in a semi-open state.

 

① Sealing Test of Floating Ball Valves: With the valve in a semi-open state, introduce the test medium into one end and close the other end. Rotate the ball several times. When the valve is in the closed state, open the closed end to check, simultaneously checking the sealing performance of the packing and gaskets; there should be no leakage. Then introduce the test medium from the other end and repeat the above test. ② Fixed ball valve sealing test: Before the test, rotate the ball several times under no-load, with the fixed ball valve in the closed state. Introduce the test medium from one end to the specified value; check the sealing performance of the inlet end with a pressure gauge. Use a pressure gauge with an accuracy of 0.5-1 and a range of 1.5 times the test pressure. No pressure drop within the specified time is considered合格 (qualified). Then introduce the test medium from the other end and repeat the above test. Next, place the valve in a half-open state, close both ends, fill the inner cavity with the medium, and check the packing and gaskets under the test pressure; there should be no leakage.

 

③ Three-way ball valves should undergo sealing tests at all positions.

 

2. Check valve pressure testing method

 

Check valve test state: For lift check valves, the valve disc axis should be in a position perpendicular to the horizontal; for swing check valves, the channel axis and valve disc axis should be in a position approximately parallel to the horizontal line.

 

During the strength test, introduce the test medium from the inlet end to the specified value, close the other end, and check for no leakage from the valve body and valve cover; this is considered合格 (qualified). The sealing test involves introducing the test medium from the outlet end and checking the sealing surface at the inlet end. No leakage at the packing and gaskets indicates a pass.

 

3. Pressure Testing Method for Pressure Reducing Valves

 

① The strength test of pressure reducing valves is generally conducted on a single-piece basis followed by assembly, or it can be conducted after assembly. Strength test duration: 1 minute for DN < 50mm; greater than 2 minutes for DN 65-150mm; greater than 3 minutes for DN > 150mm. After the bellows is welded to the assembly, a strength test should be conducted using air at 1.5 times the highest pressure after the pressure reducing valve.

 

② The sealing test is conducted using the actual working medium. When testing with air or water, the test should be conducted at 1.1 times the nominal pressure; when testing with steam, the test should be conducted at the highest permissible working pressure at the operating temperature. The difference between the inlet and outlet pressures should not be less than 0.2 MPa. The test method is as follows: After setting the inlet pressure, gradually adjust the valve's adjusting screw so that the outlet pressure can change sensitively and continuously within the maximum and minimum range, without any stagnation or jamming. For steam pressure reducing valves, after the inlet pressure is adjusted, close the downstream shut-off valve. The outlet pressure should be at its highest and lowest values. Within 2 minutes, the increase in outlet pressure should meet the requirements of Table 4.176-22. Simultaneously, the downstream pipeline volume should meet the requirements of Table 4.18 to be considered合格 (qualified). For water and air pressure reducing valves, after the inlet pressure is set, when the outlet pressure is zero, close the pressure reducing valve and conduct a sealing test. No leakage within 2 minutes is considered合格 (qualified).

 

4. Pressure Testing Method for Butterfly Valves

 

The strength test for pneumatic butterfly valves is the same as that for gate valves. For the sealing performance test of butterfly valves, introduce the test medium from the medium inlet end. The butterfly plate should be open, and the other end closed. Inject pressure to the specified value. After checking that there is no leakage at the packing and other seals, close the butterfly plate, open the other end, and check that there is no leakage at the butterfly plate seal to be considered合格 (qualified). Butterfly valves used for flow regulation do not require a sealing performance test.

 

5. Pressure Testing Methods for Plug Valves

 

① For strength testing of plug valves, the medium is introduced from one end, the remaining passages are closed, and the plug is rotated sequentially to each fully open working position. No leakage is observed in the valve body if the valve is合格 (qualified).

 

② For sealing tests, for straight-through plug valves, the pressure inside the cavity should be equal to the pressure at one end of the passage. The plug is rotated to the closed position, and the test is performed from the other end. Then, the plug is rotated 180° and the test is repeated. For three-way or four-way plug valves, the pressure inside the cavity should be equal to the pressure at one end of the passage. The plug is rotated sequentially to the closed position, with pressure introduced from the right-angle end, and the test is performed simultaneously from the other ends.

 

Before testing, a layer of non-acidic dilute lubricating oil may be applied to the sealing surface of the plug valve. No leakage or expanding water droplets are observed within the specified time if the valve is合格 (qualified). The test time for plug valves can be shorter, generally 1-3 minutes according to the nominal diameter.

 

Plug valves used for gas should undergo an airtightness test at 1.25 times the working pressure.

 

6. Pressure Testing Method for Diaphragm Valves

 

For the strength test of diaphragm valves, introduce the medium from either end, open the valve disc, and close the other end. After the test pressure reaches the specified value, check for leaks in the valve body and cover; no leakage indicates acceptance. Then, reduce the pressure to the sealing test pressure, close the valve disc, and open the other end for inspection; no leakage indicates acceptance.

 

 

7. Pressure Testing Method for Gate Valves and Throttle Valves

 

For the strength test of gate valves and throttle valves, the assembled valve is usually placed in a pressure testing frame. The valve disc is opened, and the medium is injected to the specified value. Check for sweating and leaks in the valve body and cover. Strength tests can also be performed on individual components. Sealing tests are only performed on gate valves. During the test, the valve stem of the gate valve is vertical, the valve disc is open, and the medium is introduced from the bottom end of the valve disc to the specified value. Check the packing and gaskets; after passing the test, close the valve disc and open the other end to check for leaks. If both strength and sealing tests are required for the valve, the strength test should be performed first. Then, the pressure should be reduced to the specified value for the sealing test, and the packing and gaskets should be checked. Next, the valve disc should be closed, and the outlet end opened to check for leakage at the sealing surface.

 

8. Gate Valve Pressure Testing Method

 

The strength test for gate valves is the same as for globe valves. There are two methods for the sealing test of gate valves.

 

① Open the gate to raise the pressure inside the valve to the specified value; then close the gate, immediately remove the gate valve, and check for leakage at the seals on both sides of the gate, or directly inject test medium into the plug on the valve cover to the specified value and check the seals on both sides of the gate. This method is called intermediate pressure testing. This method is not suitable for sealing tests on gate valves with a nominal diameter of DN32mm or less.

 

② Another method is to open the gate to raise the valve test pressure to the specified value; then close the gate, open one blind flange, and check for leakage at the sealing surface. Repeat the above test until the valve passes the test. The sealing test of the packing and gaskets of pneumatic gate valves should be conducted before the gate sealing test.

 

9. Pressure Testing Methods for Safety Valves

 

① The strength test of safety valves, like other valves, uses water. When testing the lower part of the valve body, pressure is introduced from the inlet end (I=I), and the sealing surface is closed; when testing the upper part of the valve body and the valve cover, pressure is introduced from the outlet end (E=I), and the other ends are closed. No leakage from the valve body and valve cover within the specified time is considered合格 (qualified).

 

② For sealing and constant pressure tests, the media generally used are: saturated steam for steam safety valves; air for valves using ammonia or other gases; and water for valves using water and other non-corrosive liquids. Nitrogen is often used as the test medium for safety valves in some important locations.

 

The sealing test is conducted at the nominal pressure value, and the test is performed at least twice. No leakage within the specified time is considered合格 (qualified). There are two methods for leak detection: First, seal all connections of the safety valve by sealing thin paper with grease on the outlet flange. If the paper bulges, it indicates a leak; if it doesn't, it's合格 (qualified). Second, seal a thin plastic sheet or other plate with grease on the lower part of the outlet flange, fill with water to seal the valve disc, and check for bubbles in the water; this indicates合格 (qualified). The safety valve's set pressure and reseating pressure tests should be performed at least three times; compliance with regulations is considered合格 (qualified). For various performance tests of the safety valve, refer to GB/T 12242–1989 "Safety Valves - Performance Test Methods".

 

 

Valve Pressure Testing Management Regulations

 

1. All valves should undergo a visual inspection after unpacking, including ensuring the nameplate on the valve body is complete, product quality certificates are present, the valve is in the closed position, there is no damage to the flange surface or other damage, no dirt, and protective caps at both ends.

 

2. Operators should be familiar with the operation of the pressure testing bench.

 

3. Valve pressure testing procedures should be thorough. Operators should be familiar with the safety hazards during valve pressure testing and reversing processes and have corresponding preventative measures in place. 4. The valve pressure testing procedure is as follows: valve body strength test, top seal test, and sealing test.

 

(1) For the valve body strength test, water is used as the medium, and the pressure is 1.5 times the nominal pressure of the valve. The pressure holding time is 5 minutes. No dripping or dampness is acceptable.

 

(2) For the valve top seal test, water is used as the medium, and the pressure is 1.5 times the nominal pressure. The pressure holding time is 15 seconds for DN≤50, 60 seconds for 65≤DN≤300, and 120 seconds for DN≧350. No leakage is acceptable.

 

(3) For the valve sealing test, a low-pressure sealing test is conducted. Air (for gate valves) is used as the test medium, and the pressure is 0.6 MPa. The pressure holding time is 15 seconds for DN≤50, 60 seconds for 65≤DN≤150, and 120 seconds for DN≧200. The permeation rate meets the requirements.

 

(4) After the pressure test is passed, the water in the valve cavity should be dried with compressed air in a timely manner. (5) Valves that pass the pressure test should be marked with a √, and valves that fail should be marked with an ×.

 

(6) After the pressure test, valves should be stacked separately according to their model and specifications, with unqualified valves stacked separately. Each stacking area should have a clearly marked sign. After the pressure test, the valves should be resealed, and the stacking area should be covered with tarpaulin for protection.

 

(7) After the valve pressure test, a "Valve/Fit Test Record" should be filled out promptly according to the device, with the purchase contract number on the valve body entered in the model column.

 

(8) For valves that pass the test, a "Valve Issuance Record" must be filled out and signed by both the issuing and receiving parties.

 

(9) A separate "Unqualified Valve Information Ledger" must be established for unqualified valves.