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Seat leakage is defined as leakage that is internal to a valve-between the inlet and outlet sides of the valve-when the valve is in its closed position. It is not limited to leakage across the valve seat, but also encompasses all leakage across the valve trim when the valve is in the closed position. Leakage across internal trim seals, such as piston rings, and across trim-to-body seals, such as gaskets, can be counted as seat leakage.
It is important to note that, while leakage through valve stem packing is of growing concern in the industry, governing industry standards address this type of leakage separately and do not consider it to be a form of seat leakage.
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What is pop up test in safety valve?
it is the pressure test used to determine the operating pressure of the pressure relief valves (CDTP).
Why back seat test is not applicable for ball valves?
Because ball valves stem can't rise. It turns 90° but it doesn't rise. Back seat test ( appicable for gate and globe valves only) can be carried out by means of the full opening of the valve. Once the valve is in full open position the stem should be in contact with the bonnet ( generally hardfaced on that area) , in a manner that a sealing between bonnet and stem allows the packing to be replaced with the pressure inside the valve. Of course this is possible only because the stem rises. In the ball valves ( standard) the stem only rotate 90° , then the back seat test can't be done.
What is the acceptance value of leakage current in HI POT test?
A HIPOT test, or a dielectric test, is designed to ensure there is no breakdown when a device under test has a high voltage applied to it, which means that it is a simple pass or fail test with no requirement for data. Requirements in safety standards may require the testing of leakage current, however, so the best example of calculating the accepted leakage current is: If you apply 1000 volts to the device under test and adjust the tester until there is a breakdown, if the products resistance is below 120,000 ohms the maximum leakage current allowed is 8.333 mA (This is calculated using the formula 1000/120,000 which is aqual to 8.333mA).
How do you test leakage on equipment?
by measuring the insulation resistance then by usig the formula for finding leakage current leakage current =voltage applied /resistance measured by megger.
What are the standards for safety valves-?
safety valve in accordance with the requirements of Article VIII of the ASME code for pressure vessel applications, which is within 10% overpressure that opens and closes in 7%.
