I've got a 900mm ball valve with about 60 bar in the line. The fluid is Methane. I've got a problem in that it doesn't seal - I suspect the seal is shot. I want to quantify the leakage rate across the valve seat.
xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx The valve has a 25mm nominal bore vent pipe attached to the ball cavity with a valve{no1} to close it off. Above valve 1 there is 150 mm of pipe with a gauge connected via a tee with another valve {no2} above it. Above this valve i have 2m of vent pipe (25mm) open to atmosphere. imagine the attempt at a sketch below orientated thru 90 degrees.
! ! O gauge ! line pressure!
----------------- atmos==valve2===="=====Valve1======[ ball valve ] --
--------------- ! line pressure! ! !
If I open valve 1 I get line pressure - 60 bar- at the gauge. when I then open valve 2 the pressure at the gauge drops almost instantly to to 27 bar. At the vent I see 'stacked diamond' shapes in the gas jet. [Underexpanded?? Sonic velocity?? Could I assume the Velocity to be about 330 m/s?? ] after about 2 minutes of constant venting the pressure at the gauge falls to
14 bar and the jet takes on a sharp cone shape. I never decrease below 14 bar at the gauge and maintain 60 bar in the line outboard of the valve seats. If I close valve 2 I regain line pressure at the gauge in about 10 minutes.I presume that the hole in the valve seat is going to be proportional to the bore of the vent pipe and is less than the area of the pipe bore because the pressure falls off. Can I establish a (rough) flow rate through the pipe from the info given? ============================================================================ ================= supplementary info... I cannot remove the valve from the line to test and cannot reduce the line pressure significantly in any way. Valve 1 is fixed and has a port 1"NPT on the discharge side. I have no equipment other than pressure gauges and standard pipe fittings to hand to construct a device for measurement. I dont have an orifice plate or any similar equipment I can connect into the vent line. ============================================================================ =================
any suggestions??
SS.