Difference between directional control valves and pressure control valves
Answers
What is difference between pressure control valve and flow control valve?
The difference is exactly how it sounds. A pressure control valve (PCV) opens and closes based on the set point predetermined by an engineer. This is usually controlled using a pressure transmitter (PT). The PT is basically an electronic pressure gauge that sends signals to the PCV and tells it whether or not there is enough pressure entering the equipment and the PCV opens or closes to compensate.
The flow control valve (FCV) is exactly the same except it gets it’s signals from a flow transmitter (FT). Just like the PT, an FT is basically a flow meter that is able to communicate with a related valve. Again, like the PCV, the FCV opens or closes based on the required flow and the signals it receives from the FT.
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In general, in my times, a Pressure Control Valve was used for gases, including hydro pneumatic systems and similar stuff like jockey pumps on firewater systems, were you need to keep a pressure to obtain a desired flow. The example before of the Argon for a welder, last time I checked you control the pressure of the gas fed to the nozzle. At a particular pressure you know that you will get the adequate cover if Argon.
Flow control valve were made in reference to liquids. In particular when the flow is critical, like for chemicals or other process situations. The flow control could be conected to a valve, a gate or to a recirculation or to the control of a pump, in particular I remember variable speed positive displacement pumps.
In a way you end up controling flow of gases with a PCV; but a flow control valve can be a gate on a channel.
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Ultimately, pressure and flow are not independent characteristics of fluid transport. You can’t change one without changing the other. But what you can do is monitor and control one, subjugating the other to follow. Pressure and flow control valves can look almost indistinguishable sometimes, except for the sensing mechanism - which is monitoring the variable you’re interested in controlling. Ultimately, most valves operate by principle of variable orifice or variable timing (fast pulsed valves, PMW, only for very small valves)
Pressure control valve will control pressure i.e. it compensates pressure as per requirement whereas in flow control, it will direct the flow of fluid.
“a pressure regulator regulates the pressure from upstream to required pressure downstream” Most of the time it is the other way round. You need backpressure for a regulator to work. “theoretically, doesn't one regulate the pressure to induce a specific flowrate” Yes. A flow control device can be as simple as your bath tap to one that compensates for pressure and temperature. “I would assume, makes it more difficult to regulate the flow of a gas compared to liquid.” Control of the flow of air is common. Welders often have a flow control to control the flow of argon.
a pressure control valve will control the pressure of air in the mechanism, whereas a flow control valve will control the flow of liquid in the system.
Pressure control reliefs pressure from the system. A flow control, control's pressure allowable coming from the system requirements.
The flow or movement of a material whether gas or liquid is metered with respect to the quantity with a flow control valve. This valve may be either manual or automatic.
The pressure control valve measures the pressure value of the quantity of a gas or liquid as it passes. This valve also may be either manual or automatic.
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comprise a mechanism that opens the valve above a predetermined pressure threshold, the pressure at the outlet remaining substantially constant while the flow increases dramatically after valve opening. Almost all passive valves on the market or valves in the human body (cardiac valves...) are based on this principle.