Technomech Engineering

Hydraulic Valves

What is a directional control hydraulic valve, and for which application do you need it?

Directional control valves can control the start, stop and change in the flow direction of a pressure medium (i.e. hydraulic oil). For this reason, they are also referred to as switching valves. Directional control valves are available as a spool, poppet, or rotary slide valves. Rotary slide valves, however, are no longer commonly used due to low operating pressure (up to 70 bar). Directional control valves without proportional control are referred to as switching valves.

Directional control valves control the start, stop and change in the flow direction of a pressure medium

The function of a directional control valve is determined by the number of working ports (excluding control ports) and the number of spool positions. A directional control valve comprises at least two spool (switching) positions and two working ports. The most common directional control valve is a 4/3-way valve, which means the valve has four working ports and three spool positions, by DIN ISO 1219.

Types Of Durectional Control Valves:

What is a pressure control valve?

Every pressure control valve switches (or controls) at a predetermined pressure setting. The switching pressure is generally a variable setting on the valve itself. A change in position of the pressure control valve (i.e. open or closed) occurs either gradually (by control) or suddenly (by switch). Pressure shut-off valves and pressure sequence valves are hydraulic valves with a fixed throttle whereas relief and reducing valves are hydraulic valves with a variable throttle.

Pressure valves are hydraulic valves that gradually (control) or suddenly (switch) change in position.

The most common types of pressure control valves are the pressure relief valve and the pressure reducing valve. Pressure relief valves control the system pressure by relieving part, or all, of the flow to tank. Pressure reducing valves reduce the pressure supplied to a sub-system of a hydraulic system. Sequence valves are used to direct the flow to a secondary circuit. Unloading valves are used to direct flow to tank at pre-set system pressure.

Types Of Pressure Control:

What is a proportional hydraulic valve and for which hydraulic applications do you need one?

Proportional hydraulic valves are able to control the opening to flow proportionally instead of gradually, as is the case for most standard hydraulic valves. The simplest type of proportional hydraulic valve is a variable throttle controlled by a manual lever. When your hydraulic application requires a very accurate control of the flow, hydraulic valves may be equipped with advanced control electronics with integrated measuring and feedback devices.

Proportional control valves are hydraulic valves that give you very accurate control of flow and pressure.

Proportional and servo hydraulic valves are usually classified as high-performance valves. This distinction gives an expected indication of performance, which tends to generalise the true differences between various types of servo and proportional hydraulic valves. Each type has its own unique performance characteristics either in controlling pressure or controlling flow. These hydraulic valves may be used to perform a directional control, pressure control or flow control function.

Types Of Porportional Control:

What is a flow control hydraulic valve and for which hydraulic applications do you need one?

Flow control valves manage the flow by decreasing or increasing the opening at the throttling point. This helps to determine speed of movement for the actuators. The simplest design for a flow control valve is a needle or longitudinal slot mounted in the pipeline and connected to a screw that adjusts the opening at the throttling point. These are called throttle valves due to the fixed throttle, which changes the actual flow through the valve at varying loads.

Use flow control valves to influence the speed of movement of hydraulic actuators in a hydraulic system.

The difference in pressure before and after the throttling point, i.e. the pressure drop (Δp), determines the rate of flow through the throttle valve at a particular setting. If the pressure drop over the throttling point remains the same, the flow of oil that passes the throttling point remains the same as well. This allows operation at constant speeds, regardless of the load. Pressure compensated flow control valves ensure that the pressure drop over the throttling point remains the same.

Types Of Flow Control:

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