10 Questions You Should to Know about hydraulic valves

What You Need to Know About Hydraulic Valves

Hydraulic Check Valve

The purpose of check valves within Hydraulic Power Packs and Systems is to allow fluid to pass in one direction but to prevent it from travelling the other direction, or doing what is known as a reverse flow. The device is usually added to a pipe to prevent oil from flowing backwards. When necessary the valve will close so that all backward movement of fluid is stopped.

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The hydraulic check valve has two ports. One is the inlet for the hydraulic fluid to enter and the other is an outlet. They will both operate in combination with the motor, cylinders and hydraulic pump. The valve controls the flow of fluid for the correct operation of equipment.

Hydraulic valves are available in a number of different designs. They may look like a poppet, a disc or one of the ball or plunger types. This will depend on where and how they are being used as to what style and size is used.

Most often you&#;ll find hydraulic check valves used in application such as braking systems, construction tools, lifting systems and other hydraulic systems. They are installed in systems where the backup of fluid could cause serious issues.

For example, if oil flowed backwards through a pipe, it could empty a hydraulic system back into the equipment reservoir. Even when the machine is turned off the hydraulic valve can prevent fluid from flowing through the system, keeping it full ready for the next time it is operated.

Dual Pilot Operated Check valves (abbreviated P.O.C), are check valves that can be opened by an external pilot pressure. Flow is blocked in one direction as per a standard in line check valve, but it can be opened when sufficient pressure from a pilot line is applied to the third port. The pressure required at the pilot port is normally only 1/3 of the pressure locked within the cylinder. This is determined by the Pilot Ratio (3:1 and 4.5:1) are normally available. They are regularly used with double acting cylinders to lock the system when pressure is switched off, either intentionally or by accident or failure. They can be fitted directly between ports on a ram or incorporated into a power manifold block or module. It is preferable to mount them directly to a ram with &#;hard&#; pipework as this increases the integrity of the device. If the pilot check is only required or desired on one side of a cylinder then it can be on the A or B sides, referred to pilot check on A or B.

Regular applications for pilot check valves are rear loading ramps on commercial vehicles. Balers and compactors where the load needs to be held while baling occurs. Security access bollards and blockers to stop the creeping down when the system is at rest. It is important top note that POC are not best suited to applications that have a load that that will over run when they are reversed.

Flow Control Valves

Flow control valves regulate the flow of a fluid and take many forms:

Fixed orifice: Basically a hole in a tube or an insert that fits into the hydraulic line, restricting the amount of fluid that can pass through it for a given pressure.

Adjustable orifice: The size of the effective orifice is adjustable. Common forms are inline and barrel type where the body of the valve is twisted, needle valves for fine adjustment on low flow systems. When set the adjustment can be locked. These are regularly used on lifts or tipper applications where the load is uniform.

Pressure compensating: When a load such as a cantilever passes through an arc the system pressure can vary. This causes the speed of the cylinder to change leading to potentially undesired results. To overcome this pressure compensating valve account for changes in pressure and delivers broadly uniform flow to the hydraulic actuator. In a scissor lift a high pressure is required at the initial raise and decreases as the mechanical advantage increases. The reverse is true when lowering under gravity so a compensating flow control is suited here.

Reverse flow check: On a single acting power pack the pump and motor combination are optimized to give the desired lift speed of the hydraulic cylinder. The flow control valve has an integral bypass line that allows full flow in the out direction, through a built-in check valve. When lowering the full flow oil path is checked and forced to go through the flow restriction allowing controlled descent of the cylinder.

Dual Flow Control Valve

This consists of two valves in one block. When operating a double acting ram the extend and retract speeds will differ, due to the different fluid volumes. From our control valve full flow is permitted through in one direction whereas the other side is flow controlled and/or vice versa, in this way the different valve settings will optimize the actuator speeds. A common example of this valve configuration would be a rear door on a horsebox where the door will need to close much more slowly to prevent shock and noise.

Relief Valve

A relief valve is an important control device in virtually every hydraulic system. They protect the overall system from generating a pressure that could cause mechanical failure. It is a mechanical valve that requires no external input other the applied pressure. When this excess pressure is relieved it re-seats to allow normal operation to resume. The most common type comprises a spring and plunger pushing onto a seat. If the pressure exceeds that of the spring force the oil is spilled to a volume usually the oil reservoir. The springs have adjustment ranges for example 20-100 bar and the valves can be housed in cartridge, module or designed directly into an aluminum or steel hydraulic manifold.

A hydraulic circuit may have multiple relief valves, one at the power pack end to protect the pump, another may be fitted onto a control valve circuit to relieve an induced load caused by external mechanical forces. If a hydraulic cylinder requires different relief valve settings on it full bore or annulus side then a dual relief valve module can be set to handle these needs. On the annulus side the area the oil is acting upon is smaller requiring higher pressures to exert the same force as the full bore side hence two relief valve settings are needed. One example of this is a hydropower generation sluice gate operation where something jammed in the gate such as log stops it closing.

Some terms associated with relief valve operation:
Overshoot: The pressure reading when a relief valve operates to bypass fluid. (It can be two times the actual setting.)
Hysteresis: The difference in pressure when a relief valve starts spilling some flow (cracking pressure) and when full flow is passing.
Stability: pressure fluctuation as the relief valve is bypassing at its set pressure.
Reseat pressure: The pressure a relief valve closes at after it has been operating.
Counterbalance valves are fundamentally a relief valve that is fitted in an application to generate back pressure in a system. They are normally used for &#;counterbalancing&#; a load to stop it from running away during lowering. The valve is usually set at 30 percent higher than the pressure induced by the load.

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A built in check valve allows flow in the reverse direction (i.e. to by-pass the counterbalance valve when lifting the load). It should be noted that both sides of the valve will be subjected to full pressure, this is not possible on all relief valve designs. In Figure 1 the counterbalance valve has an integral check valve. When counterbalancing the return path must have a low back pressure to tank, as this will be additive to the valve setting.

What are hydraulic valves and why are they crucial?

Hydraulic valves control and regulate fluid flow, ensuring the system operates efficiently and effectively. They are essential components that control the flow and pressure of hydraulic fluid and ensure that the machinery operates as needed.

For example, the construction sector, predicted to grow to £476.6 billion by , relies heavily on hydraulic systems for equipment such as excavators and cranes. Reliable hydraulic valves offer enhanced performance and reduce the risk of machinery breakdowns.

Safety is another key consideration. According to the Health and Safety Executive (HSE), mechanical equipment failures, often involving hydraulic systems, are a significant cause of workplace accidents. Using high-quality, well-maintained hydraulic valves can minimise these risks and promote a safer working environment.

Types of hydraulic valves

&#; directional control valves

These valves manage the path of hydraulic fluid by ensuring actuators move in the correct direction. They play a vital role in equipment like bulldozers and forklifts which require precise control for safe and efficient operation.

&#; pressure control valves

These regulate fluid pressure to prevent system overload. In manufacturing, where pressure stability is crucial for automated machinery, these valves are indispensable. With manufacturing accounting for 10% of the UK&#;s GDP, reliable pressure control ensures smooth operations and minimises the risk of costly downtime.

&#; flow control valves

Flow control valves manage the fluid flow rate affecting actuator speed. These types of valves are essential in agriculture where tractors and harvesters need regulative fluid control for optimal performance.

&#; proportional valves and servo valves

These advanced valves offer precise control of fluid flow and pressure. They are used primarily in precision Industries such as aerospace and robotics where accuracy is paramount.

How does a hydraulic flow valve work?

A hydraulic flow valve controls the rate of fluid movement in a system by regulating the flow it determines the speed at which actuators, like cylinders or motors, operate. When the valve opens, more fluid is allowed to flow and therefore increases the actuator&#;s speed.

How does a hydraulic control valve work?

Hydraulic control valves adjust the flow and pressure of fluid ensuring the systems maintain the desired performance levels under varying operational conditions. In particular, these valves are important in the oil and gas sectors as they manage the pressure in pipelines and drilling equipment.

The importance of choosing the right hydraulic valves

Ensuring you have the right valve is vital. They not only ensure that systems operate efficiently but they also reduce the likelihood of breakdowns and promote workplace safety.

The economic benefits of choosing quality valves are also clear as they lower maintenance costs, prevent expensive down times and can boost productivity.

10 essential things you should know about hydraulic valves;

1. They are essential for controlling and regulating the flow pressure and direction of hydraulic fluid.
2. There are several types of hydraulic vowels including directional control valves, pressure control valves and flow control valves. Each type serves a specific function.
3. Hydraulic valves play a crucial role in safety by ensuring pressure and fluid flow they prevent system overloads and potential equipment failures.
4. Properly functioning hydraulic vowels can significantly increase the efficiency of hydraulic systems.
5. Hydraulic valves are used widely across a broad spectrum of industries including but not limited to construction agriculture manufacturing and Aerospace.
6. Advanced valves like proportional and servo valves provide highly accurate control of flow and pressure.
7. Hydraulic valves help extend the lifespan of your machinery by reducing the wear and tear of components.
8. Hydraulic valves are made from durable materials like stainless steel, brass, and cast iron.
9. Quality hydraulic valves have a direct impact on the economic performance of industries by minimising unplanned equipment downtime.
10. Innovations in hydraulic valves are constantly evolving with smart valves and electronic controls helping to improve system responsiveness and efficiency.

If you are considering upgrading or maintaining your current hydraulic systems, make sure you consult industry experts and invest in high-quality valves.

Contact HOS today to speak to one of our team to discuss your needs.