Difference Between Flow Control Valve and Pressure Control Valve

Their names indicate their working principle. This means the feedback is for one the flow and for the other the pressure. In all hydraulic regulating valves the measure of the result (the feed back) is a force which is compared with a spring preload or an electromagnetic farce generated by a solenoid.

Those are basic general principles for your question you find the answers in ALL technical brochures manufacturers as Parker or Rexroth or other put at customer's disposal.

Application? A flow control valve is there to control the flow, and a pressure control valve is there to control the pressure. The answer is written in the question for the careful reader.

thanks,

when you are controlling the flow by using flow control valve and is that not goin to affect the pressure?? and vice versa too??

and as of my knowledge in both the cases we are reducing the area of the pipe to control the flow or pressure isn't it!! if not then whats the difference between those two control valves with respect design!?

regards,

Prakash

If you think a bit even in the situation you mention it is a "flow control" since it lets "flow" a fluid to the tank or the sink. Without opening the path for this "flow" the pressure would not decrease.

But this is NOT an application in hydraulics. In hydraulics the pressure control valve is a device which compares the pressure to a spring force (in general) and modifies in a continus mode the opening to the tank so that, in case of a constant flow pump, only part of delivery goes to the system. The type you mention is a "pressure limiter" which is closed as long as pressure is under a threshold and opens only when it goes over. This cannot be considered as a "pressure control valve" since it does not maintain it constant it only serves as safety.

Thanks for the reply.

From your declaration I understood that "Pressure control valve" is completely different from the "Pressure relief valve" but at the same time i dint get how this pressure control valve designed differently and works differently from the Flow control valve.

I want to mention one thing here about why i got this confusion.

For example i'm designing a hydraulic power pack, in that i have used a gear pump with fixed speed motor and that delivers a known/fixed duty point and i want use that output for different applications like Hydraulic splitter, Hydraulic Driller, Hydraulic Breaker etc by changing both flow and pressure.

(ex. system (HPP) output is 170 bar:20USGPM,

required flow and pressure for different applications are 100 bar:20USGPM, 100 bar:10USGPM etc.)

here is the question, i.e, how can i control both flow and pressure of the power-pack output??

is that by using both the pressure control valve and the flow control valve serially!! or is there any other method to control these parameters?! if i consider the first case then does flow control valve varies the pressure while controlling the flow, likely does pressure control valve affects the flow!! if this is the case then how can i control both flow and pressure in a single line per the requirement.

Best Regards,

Prakash

As I mentioned above hydraulic pumps are VOLUMETRIC pumps which means that for a given rpm a specific flow will be delivered. Delivered flow will ONLY be modified by the amount of internal leakage which is more or less proportional to pressure.

Flow can thus be increased or decreased ONLY by rpm changes. It is also possible with a valve to divert part of flow to tank thus reducing the flow to the motor (cylinder or other types). If this control is piloted by the user's pressure then you obtain a flow which will depend on the load. The arrangement will maintain pressure at set level.

The other control possibility is to use flow control 3 ways valves which according to set value will allow to motors a flow independent of load requirements.

In the applications you mention what you need is a flow control with a pressure safety valve thus a pressure relief valve. What you have not yet understood is that in volumetric systems pressure depends only on load resistance.

Using a fixed gear pump you have a drawback due to the back-flow at the user's pressure level which will heat oil in the reservoir. If the operation takes more time then oil can get too hot for the seals and you risk extrusions and losses. You should compute the thermal time constant of your reservoir and increase as much as possible the heat transfer to environment.

PW,

You don't miss many, but on this one I think you are a little off.

In reality all Control Valves control flow.

The problem is NOT what they modify but which the scope of the modification. This is the reason I mentioned the "feed-back" since one reacts to a pressure feed-back and the other to a flow feed-back.

Since hydraulic systems are, let say in most if not in all cases, volumetric systems the control which ever the scope is will affect the flow.

Flow control will adjust pressure to maintain flow.

Pressure and flow are two different things. a flow control valve controls the amount of flow to a device i.e. steam turbine control valves. a pressure reducing valve reduces pressure to the user i.e. regulator on an airsystem used to drop instrument air to a usable pressure.