Engineering Essentials: Pressure-Control Valves

Pressure-control valves are found in virtually every hydraulic system, and they assist in a variety of functions, from keeping system pressures safely below a desired upper limit to maintaining a set pressure in part of a circuit. Types include relief, reducing, sequence, counterbalance, and unloading. All of these are normally closed valves, except for reducing valves, which are normally open. For most of these valves, a restriction is necessary to produce the required pressure control. One exception is the externally piloted unloading valve, which depends on an external signal for its actuation.

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Relief valves

Most fluid power systems are designed to operate within a preset pressure range. This range is a function of the forces the actuators in the system must generate to do the required work. Without controlling or limiting these forces, the fluid power components (and expensive equipment) could be damaged. Relief valves avoid this hazard. They are the safeguards which limit maximum pressure in a system by diverting excess oil when pressures get too high.

Cracking pressure and pressure override &#;The pressure at which a relief valve first opens to allow fluid to flow through is known as cracking pressure. When the valve is bypassing its full rated flow, it is in a state of full-flow pressure. The difference between full-flow and cracking pressure is sometimes known as pressure differential, also known as pressure override.

In some cases, this pressure override is not objectionable. However, it can be a disadvantage if it wastes power (because of the fluid lost through the valve before reaching the maximum setting). This can further permit maximum system pressure to exceed the ratings of other components. (To minimize override, use a pilot-operated relief valve.)

Relief valves are either direct-acting or pilot-operated.

Everything You Need to Know About Essential Hydraulic Systems Components

No matter what type of hydraulic system and where it is used&#;construction vehicles, manufacturing equipment, mobile systems, etc.&#;they will all share similar hydraulic parts and components. It is essential that you know the characteristics of each of these components so you can better understand how they allow the system to function correctly.

 

#1. Hydraulic Fluid Reservoir Tank

The hydraulic fluid that flows through the system is stored in the hydraulic fluid reservoir. Therefore, the reservoir should not be in any way open to the elements so as to prevent contaminants from getting into the hydraulic system. Contaminants will affect system performance and could lead to system failure.

The hydraulic fluid that flows through the system is stored in the hydraulic fluid reservoir. Therefore, the reservoir should not be in any way open to the elements so as to prevent contaminants from getting into the hydraulic system. Contaminants will affect system performance and could lead to system failure.

 

#2. Hydraulic Hoses and Pipes

Various hoses and pipes are used to transmit the hydraulic fluid through the system to different parts and components.

 

#3. Hydraulic Pumps

To energise the fluid in the system, hydraulic pumps are required. The inlet side of the pump will be connected to the reservoir.

Pumps work in conjunction with hydraulic valves and are a necessary part of the system&#;s ability to convert mechanical energy into hydraulic energy. Depending on the type of system, you could have gear pumps, piston pumps, or vane pumps or a combination of different pumps.

 

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#4. Power Source

There needs to be some sort of power source to run the system. For example, in mobile hydraulic systems is often a diesel or a petrol engine, such as on construction vehicles, lorries, and farm equipment. As the engine runs, it supplies mechanical power to the hydraulic pumps, which then supply hydraulic power via hydraulic valves to hydraulic motors and other hydraulic actuators, parts, and components.

For non-mobile hydraulic systems, the most common power source is an electric motor. As the electric motor runs, it mechanically powers the hydraulic pumps to push hydraulic fluid through the system.

 

#5. Hydraulic Actuators

Some of the most common types of hydraulic actuators are hydraulic motors. A hydraulic motor is responsible for converting hydraulic flow and pressure into mechanical energy to provide the necessary torque and rotational power to perform the desired functions.

Motors come in different sizes and configurations, such as piston motors, orbital motos, gear motors etc. The oil flow and motor displacement determines the motor&#;s speed (RPM). As a result, valves can control and regulate the amount of force and mechanical energy created.

Another type of hydraulic actuator found in hydraulic systems is the hydraulic cylinder. As the cylinder rods move in and out of their bores, they also help convert hydraulic flow and pressure into mechanical energy.

 

#6. Valves

Different types of valves can be used in the hydraulic system, such as:

• Directional Control Valves
• Pressure Relief Valves
• Flow Control Valves

Directional control valves allow for the control of individual or groups of actuators in a system.  The directional control valve may incorporate other valves, such as pressure relief and flow control into the same assembly. A pressure relief valve regulates pressure by opening and closing at specific pressure levels. Flow control valves regulate the flow rate by adjusting the orifice size through which the fluid passes.

 

#7. Hydraulic Fluid Filters

There are normally various types of hydraulic fluid filters installed in different locations throughout the system. For instance, there should be filters in the reservoir to help remove contaminants both returning from the system and the return filter and before supplying the pump suction filter. Some systems will also have pressure filters at various stages in the system to further help remove contaminants.

 

#8. Hydraulic Fluid

Hydraulic fluid is necessary for the system to function correctly. There are different types of hydraulic fluids for various operating conditions and environments. Therefore, it is crucial to use the right type of fluid in your hydraulic system. If you use the wrong fluid, it can cause operational problems that lead to system failure.

Aside from these common parts and components, there are also hydraulic seals, fittings, O rings, and accumulators you should be aware of when they are used as part of your hydraulically powered system.

 

White House Products, Ltd. for the Parts You Need

By having a better understanding of the common hydraulic system components and parts, you gain a better understanding of how the system functions and operates. To find hydraulic system parts and components, including pumps, motors, cylinders, and custom-built solutions for specific applications, please contact White House Products, Ltd. at +44 (0) today!

The company is the world’s best hydraulic flow control valve supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.

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