bloudup008
Mechanical
can someone please explain how does a pressure control/regulating valve regulate the static pressure downstream (at no flow condition)
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pressure control valve: static pressure
- Thread starter bloudup008
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Let's say you are flowing through the system and you stop the downstream flow for some reason.
Flow will continue through the control valve. The flow into your piping system with no outlet flow will cause the pressure to rise. That rise in pressure will cause the control valve loop to start to close the valve to maintain set-point (from your question, I'm assuming your control valve is for downstream pressure control).
How fast the valve closes and what the final pressure for the system is is a function of the control loop tuning and system size but once it's closed, the pressure can't decrease until you remove material from downstream of the valve. Also, the pressure will likely continue to increase unless your control valve is a bubble tight shut-off which I suspect is unlikely.
This is true for both a gas and liquid system but since a liquid system is essentially incompressible in many cases, the downstream pressure will increase much faster than for a gas.
Flow will continue through the control valve. The flow into your piping system with no outlet flow will cause the pressure to rise. That rise in pressure will cause the control valve loop to start to close the valve to maintain set-point (from your question, I'm assuming your control valve is for downstream pressure control).
How fast the valve closes and what the final pressure for the system is is a function of the control loop tuning and system size but once it's closed, the pressure can't decrease until you remove material from downstream of the valve. Also, the pressure will likely continue to increase unless your control valve is a bubble tight shut-off which I suspect is unlikely.
This is true for both a gas and liquid system but since a liquid system is essentially incompressible in many cases, the downstream pressure will increase much faster than for a gas.
Can you either restate the question, or provide more information.
On the face of it, this does seem like a "trick" question.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
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On the face of it, this does seem like a "trick" question.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
TD2K pretty well said it all. If its still not clear, maybe this will help,
When the downstream pressure finally reaches the set pressure, the valve closes completely and all flow across the valve stops (except for the aforementioned leakage).
When the downstream pressure finally reaches the set pressure, the valve closes completely and all flow across the valve stops (except for the aforementioned leakage).
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bloudup008
Mechanical
thks everyone
can I consider PRV effective for the control of static pressure?
can I consider PRV effective for the control of static pressure?
bloudup008,
The quick answer is no. A PRV (Pressure Relief Valve) will only prevent the pressure from reaching a setpoint. It prevents overpressure. A PRV will not control to a setpoint (the pressure may be lower). In any case, a PRV should not be used for control - it is considered a "safety" device.
Can you describe more in detail what it is you are trying to do? It is more efficient than asking what each of the devices are used for.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
The quick answer is no. A PRV (Pressure Relief Valve) will only prevent the pressure from reaching a setpoint. It prevents overpressure. A PRV will not control to a setpoint (the pressure may be lower). In any case, a PRV should not be used for control - it is considered a "safety" device.
Can you describe more in detail what it is you are trying to do? It is more efficient than asking what each of the devices are used for.
"Do not worry about your problems with mathematics, I assure you mine are far greater."
Albert Einstein
Have you read FAQ731-376 to make the best use of Eng-Tips Forums?
Perhaps the question pertains to a self-contained pressure reducing regulator. These generally only provide proportional control with some offset. They open more when the downstream pressure is low and close when the downstream pressure matches the set point. Some regulators have a vent that relieves overpressure in a non-flowing or high downstream condition. This is not acceptable within many gas products and industries.
You >could< embellish the question a bit. Better questions get better answers.
If you use a regulator that has rubber seats it is supposed to shut off bubble-tight and to prevent the downstream pressure from exceeding setpoint.
As JLSeagull mentioned, some regulators have relieving devices built-in. These are almost universal on the 1/4" filter-regulators used as point-of-use regulation. Fisher 67FR, Masoneilan 80-4, or the one they sell at Home Depot for use with an airbrush...That way if you have it all piped up and you are winding the adjustment knob to set the pressure,and you pass the setpoint, it will relieve if you unwind the set knob a bit. But if they leak through, the relief feature also will keep the downstream pressure from exceding set. Thjat's OK on air, but if you have the regulator on nitrogen you may displace the local atmosphere and create a hazard, or if the regulator is on something flammable like Natural Gas, there may be a potential for a kaboom.
Steam regulators can't have soft seats because of temperature, but as long as they leak more slowly than the steam condenses in the downstream piping, the pressure will not rise, and the steam traps will take out the condensate.
If you use a regulator that has rubber seats it is supposed to shut off bubble-tight and to prevent the downstream pressure from exceeding setpoint.
As JLSeagull mentioned, some regulators have relieving devices built-in. These are almost universal on the 1/4" filter-regulators used as point-of-use regulation. Fisher 67FR, Masoneilan 80-4, or the one they sell at Home Depot for use with an airbrush...That way if you have it all piped up and you are winding the adjustment knob to set the pressure,and you pass the setpoint, it will relieve if you unwind the set knob a bit. But if they leak through, the relief feature also will keep the downstream pressure from exceding set. Thjat's OK on air, but if you have the regulator on nitrogen you may displace the local atmosphere and create a hazard, or if the regulator is on something flammable like Natural Gas, there may be a potential for a kaboom.
Steam regulators can't have soft seats because of temperature, but as long as they leak more slowly than the steam condenses in the downstream piping, the pressure will not rise, and the steam traps will take out the condensate.
Take a look at Air l\Line Regulators and Pressure Reducing Valves in Chapter 14 of a Fluid Pwer training book at this site:
Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING
Bud Trinkel, Fluid Power Consultant
HYDRA-PNEU CONSULTING
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