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If the Static Pressure Remains Constant at the Outlet of Regulator, will the Flow Rate Vary with the Inlet Static Pressure?

for a fixed opening at the outlet of a regulator, if the static pressure at the outlet remains constant, will the flow rate increase or decrease with the increase or decrease in the inlet gas pressure? 

Jawad Waheed

• 25 Nov 2017 6:06 AM
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4 Replies

• Jeff_Welch

  

  • 28 Nov 2017 1:51 PM

  Jawad,
  In general, the greater the pressure differential, the greater the flow capacity due to the differential across the valve (potential energy). However, If you have an unbalanced style regulator, then the outlet will increase or decrease as the inlet pressure fluctuates...and depending on how the valve operates, your flow rate will be impacted by higher/lower flow rates. If your regulator is balanced, then the outlet will not fluctuate with inlet pressure but your flow rate will increase/decrease based upon the differential pressure. If your application has large inlet pressure swings, it might be beneficial to either A) use a balanced style regulator or B) use a supply regulator to send a constant inlet pressure to the controlling regulator. Option B has more sizing considerations though.

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• Jawad Waheed

  

  • 29 Nov 2017 4:51 PM

  In reply to Jeff_Welch:

  Jeff,
  for a given or set outlet pressure, the differential pressure is only and indicator of maximum flow rate capacity through the regulator, and we both know that the flow rate of the regulator can be modulated in accordance with the load. Suppose its a 2inch size regulator and we have 2 inch line downstream, at the end of which there is just a nozzle with 10 mm dia to flow the gas out to the atmoshphere..the load is fixed...so as long as the pressure to the nozzle is kept constant, the flow rate will be constant.

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• Jawad Waheed

  

  • 30 Nov 2017 3:20 AM

  In reply to Jeff_Welch:

  say if i use balanced style regulator...and the inlet pressure starts to increase so the differential pressure will increase and as you say the flow rate will increase, which means the regulator will try to put more gas in the system in the result of which the outlet pressure will increase..which will cause the regulator to self adjust to bring back the outlet pressure to the set point.. so the flow rate will come back to the previous rate at the set outlet pressure.. so i understand if the pressure at the outlet is constant, the flow rate at the outlet must be constant.. in the subcritical range..

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• Jeff_Welch

  

  • 30 Nov 2017 9:59 PM

  In reply to Jawad Waheed:

  Jawad,
  I am saying the potential to flow more through the valve increases. Increasing inlet pressure will not increase flow if the demand is being met. If I have a valve that P1- 100 psig and P2- 10 psig and my demand needed is 5000 scfh at 20% droop (outlet at q= 5000 scfh / P2-8 psig)...and all of the sudden the inlet pressure jumps to 150 psig...my demand is still 5000 scfh and my regulator will still only allow 5000 scfh into my system. Because my potential for flow is higher, the regulator plug will need operate closer to the orifice so not to allow more gas than is needed. This will result in less droop in my system, but my flow will remain the same (q=5000 scfh / p2-9 psig).

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