Pressure Decay Testing

I am working on a project in which we require to fill a vessel with compressed air to a specified pressure and then test whether or not the vessel leaks.

To this point; I have developed the HMI and PLC code to basically open a fill valve, close the fill valve and then test the pressure after 1.5 seconds.

I am using Asco bubble tight valves, ML1100 w/1762-IF4 and 836E pressure transmitter from AB.

I can make the system work on small vessels but the stabilization of the air pressure is what is undermining the project.

Anyone have any thoughts on what I can do differently???

JG

Describe what you mean by "Stabilization of the air pressure is what is undermining the project".

I would fill to a nominal value, close the fill valve, wait a bit, take a reading (almost like a tare), wait some more, and take the comparison reading.

That's what I did but the powers that be say the cycle time is too slow. I tried to pressurize to equal the set point and then cycle the inlet a couple of times to speed up the stabilization but that wasn't any faster.

Thanks for the quick reply...

The situation is that the vessel is filling similar to the way a capacitor charges - initially the difference is large so filling is easy - when the difference is small it takes longer and longer to achieve the final pressure (charge).

I have solved this in the past by having two regulators. If your target pressure is 30 psi, one regulator is set to 30 and the other is set to 35 (or some number higher than your final pressure). Start filling using the 35 psi then when you achieve 85-90% (or so) of your final value, switch to the working pressure.

Sounds like your pressure tap isn't in an optimum place to measure static pressure, sound like you have some flow losses affecting your pressure reading.

Jeffreyl.gregory,

1 Please detail the vessel sizes.
2 When you shut off the air valve to the vessel, how long do you wait before
you start the test?
3 How long is the test for each vessel?
4 How accurate is your pressure sensor and what is the Hystersis?

I did a similar project in the 90's is why i am asking.

regards,
james

I used to work for oil pipe plant, we needed to test pipes under pressure sometimes up to 10000 PSI, we have two pumps one to fill the pipe, and the other to increase pressure. When we saw water coming out of the main valve meaning pipe was full of water we close that valve, when valve was closed we started another pump either high pressure pump or hydraulic intensifier in order to reach setpoint pressure. If setpoint was 8000 psi we stopped second pump at 8100 psi, wait 10 seconds while making a graphic of pressure. There were some leaks but we knew that if the pipe was leaking then pressure dropped inmediately otherwise pipe test was ok.
In this case it seems your leaks are high enough to affect your pressure reading.

hey guyz , i want to make a machine ,in which i want to cut a piece in lengthwise and i want to do it without plc system, can anyone help me plz

This system is a complete assembly of bladeholder, workpiece clamp, alignment guides and actuator.

It should do the job for you. No PLC required.

Ken, nice job!! Looks like it should fill the bill nicely for the sodium sulphate fellow ...