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I have a 12" flow meter that uses a float on a stem and whenever gas is supplied, the initial flow spikes the float to the top and gets wedged. The flow meter is plumbed downstream of a control valve and ball valve that is being used to regulate the flow at 40 cfm. The supply side is helium that can range between 60 - 80 psig and the outlet of the meter is plumbed to a chamber at half atmosphere, ~ 400 Torr.

I'm aware that a ball valve should not be used to fine tune flow, that's why I need some clarification to properly correct this issue. I attached an image to help better explain my current setup.

enter image description here

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The flow meter needs to be installed such that it is always under pressure (in normal operation). That is it should be after the regulator but before the on/off valve. That way you will get no surge of gas entering an empty pipe and pushing up the float. It is quite a common problem.

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How is the helium line upstream of the control valve? Any constrictions? Can you mount a manometer close to the control valve? How is the 80 psig supplied? Long line or tube? I have the suspicion that initial pressure in the helium line is high, then you open the ball valve and an iniial gush of helium wedges the floater of the flowmeter.

Try to install a manometer upstream of the first valve to check.

As for your real question, I would turn the control valve all the way shut, then open the ball valve all the way, then slowly open the control valve until my desired flow is established. The control valve should give you a far finer and more linear control over flow than the ball valve.

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  • $\begingroup$ I should clarify that the control valve is just an open/close solenoid wired to a plc. I'm prepared to buy the correct equipment for flow regulating, but my over all question is should the flow meter be installed before the solenoid on the high pressure side to reduce the inrush or after on the low pressure side with a flow regulator installed before the flow meter? $\endgroup$ – Steven S. Aug 26 '19 at 1:47
  • $\begingroup$ Is the helium pressure constant? Is the flow you need constant? In that case, the direction should be ball valve - solenoid - manually operated control valve, IMO. $\endgroup$ – mart Aug 26 '19 at 18:46

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