Vacuum Testing of a 10" Angle Angle Motor Operated Globe Valve

[skipper1957]

Currently purchasing a replacement 10" angle motor operated globe valve (see attached file) with the following parameters:

- End use is a Vacuum Breaker valve off of a steam condenser.
- Designed for operation in a full vacuum service (below the disc). The design pressure is 29.5 in. HG. VAC., with the condenser operating pressure at a nominal 2.00 in. HG. ABS.

Have invoke API-598 for testing, but review of API-598 finds little guidance or direction for testing a valve like this and with these conditions.

Does anyone have any recommendations on meaningful testing criteria that we might apply to ensure valve functionality and reliability?

 

[gerhardl]

Could you please expand your explanation. I am a bit confused here.

Usually a vacuum breaker valve is operated automatic by a pressure difference, not a motor.

This is often done by a vertical inlet, and a horizontal disc as closing part.

The opening (cracking pressure) is given by the forces working on top of plate(weight of plate and outher pressure pluss 'sticking' factor) minus counteracting forces (closing springs and inner pressure)

From the drawing this seems perhaps to be also the construction here.

If this is the case you have to check the desired cracking pressure, and find a way to create the desired vacuum for this, isolating the valve and/or part of pipeline and check the cracking pressure in a series of tests, in my opinion at least three consequtive.

There should be a difference from cracking pressure down to max tolerable vacuum for the factory, as there will be a difference from cracking down to full opening (and hence full air opening).

You should also check if the valve has sufficient dimension to give the desired air inlet at full opening.

If the valve, somewhat agianst my belief, is motor operated, the procedure is the same, but including function of releasing (starting signals from instruments) and response time.

 

[skipper1957]

Mr. Gerhardt,

I appreciate your reply and eill do my best to reply to your comments. I offer:

1. The subject valve end use is a Vacuum Breaker valve off of a steam condenser, provided for and spec'd out by the Turbine Generator Supplier. It is designed for operation in a full vacuum service (below the disc). The design pressure is 29.5 in. HG. VAC., with the condenser operating pressure at a nominal 2.00 in. HG. ABS.

2. The valve does not receive an automatic signal to open or close. It is done with intention by a hand-switch. I conclude that once the circulating water pumps are shut off, and no more water is going through the condenser tubes, as well as no steam entering the condenser, a decision is made to "break condenser vacuum" - thus the reason for this valve.

3. As mentioned previously, given this scenario, normally one would pressurize (+) below the valve disc. In this I am pulling a vacuum (-). So do a set up a rig to pull a vacuum on the bottom side and see how good it is, or pressurixe the top side of the disc, or......

 

[reverman]

seems to me your best bet for testing would be to try and recreate the worst case conditions the valve will actually see.

Typically API 598 would require a high pressure hydro test with pressure under the seat for this valve.

What you might propose to the valve manufacture is ask them to do the API 598 optional low pressure closure test on the valve but with pressure above the disc.

This test will be closer to real world conditions and shouldn't be too difficult for the valve manufacture to perform thus minimizing the extra cost.