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Hydraulic Pump Pressure Versus Flow

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When you are using a hydraulic system, it is important to know the difference between the pump flow rate and the system’s pressure. 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. For example, 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.

Difference of Hydraulic Flow and Pressure

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:

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

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 would be virtually zero.

Now, let’s close the hand valve and turn the pump on. This time, the fluid travels towards 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 exit through the tank port of the valve.

The resistance exerted by a load initiates pressure in a circuit. Therefore, the difference between hydraulic pump pressure and pump flow is that the pump delivers a flow rate, and pressure results when that 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.

What Is Flow Rate?

Flow rate is how fast the fluid flows through the system. For example, when you turn the pump on, the speed of the pump will determine the flow rate. If you have a fixed-speed pump, the fluid flow rate remains constant at the maximum fixed speed of the pump. 

On the other hand, if you have a variable speed pump, then the flow rate of the fluid increases or decreases based on the speed setting on the pump.

Understanding the Relationship

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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.

As such, it will be easier to select the 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 systems, our inventory covers components to meet all your hydraulic needs.

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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