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Hydraulic Pump Pressure Versus Flow 08## August 2019

Pressure and flow are two key concepts related to hydraulic pumps and the systems they are used within. Some people mistakenly mix up these two terms and their functions. They might say their high-pressure hydraulic pump is not creating any pressure, so they need to replace it.

However, this is not an accurate assessment of the problem since the pump is responsible for flow.

Hydraulic pump pressure is created by the resistance encountered by the flow the pump creates. To better illustrate this, consider a basic hydraulic setup where you have two different paths the fluid can travel:

• A dead headed pressure relief valve with a pressure setting of—let’s say—200bar/2900psi
• A manually controlled hand valve, which you can open and shut, connected to an empty barrel

Pressure vs. Flow

If you leave the hand valve open and turn on the pump, according to the laws of physics, the flow of the fluid is going to take the path of least resistance. So, naturally, it would flow through the open hand valve and into the empty barrel and the pressure of the hydraulic fluid will be virtually zero.

Now, let’s close the hand valve and turn the pump on. This time, the fluid travels toward the relief valve, where pressure would quickly start to build since the fluid has encountered a resistance until it reaches 200 bar; the relief valve would then open and the fluid would exhaust through to the valve.

The resistance exerted by a load initiates pressure in a circuit. Therefore, the difference between hydraulic pump pressure & flow is that the pump delivers a flow rate, and pressure results when flow encounters resistance. Pressure is a measure of this resistance as a force per unit area. When one mentions the pump’s pressure rating, they’re talking about how much resistance the device is capable of handling or what it can work to overcome.

There are also different types of pressure. Each pump has a rated operating or discharge pressure. This must be equal to or above the system pressure needed to achieve optimal performance.

Understanding the Relationship

It’s important to know the difference between pressure and flow in hydraulic systems because it impacts how flow control is approached. By measuring system resistance, which indicates the pressure difference between a pump and the load, an operator can provide the proper commands to boost performance and efficiency. The relationship between hydraulic pump pressure and flow applies whether open center, constant pressure systems, or load sensing systems are used.

Understanding how flow influences pressure helps gauge hydraulic pump system performance, select appropriate power sources and motors, and know how to compensate for internal losses due to factors such as flow separation, internal leakage, and friction.

Contact White House Products, Ltd.

We are a leading supplier of hydraulic pumps, motors, valves, and other components and systems. From individual parts to complete build systems, our inventory is stocked with items of various parameters to meet your application. For assistance in selecting the right pumps, motors, and accessories for your hydraulic systems, contact White House Products, Ltd. at +44 (0) 1475 742500 today!

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