Hydraulic Valves

Abstract

Hydraulic valves are mechanical devices that are used to regulate the flow of fluid within a hydraulic circuit or system. They can be used to completely close a line, to redirect pressurized fluid or to control the level of flow to a certain area.
Hydraulic Pressure Control Valves
Hydraulic pressure control valves are used to regulate the fluid pressure that is passing through hydraulic systems to maintain that pressure at desired levels as determined by the system operator. Fluid systems are typically designed for operation at a set range of pressures. These types of valves serve a key role to prevent rises in pressure that may result in leaks of hydraulic fluid or the bursting of pipes and tubing. They are also used to maintain a set pressure in a part of a hydraulic circuit.

The various types of pressure control valves used in hydraulic systems include relief valves, reducing valves, sequence valves, counterbalance valves, and unloading valves.

Hydraulic Flow Control Valves
Hydraulic flow control valves are used to adjust the flow rate of hydraulic fluid in a hydraulic system. These valves have a port that is able to be adjusted so that the flow area may be changed to provide an alteration in the flow rate through the valve. An example of how this type of hydraulic valve would be used is in control circuits for devices such as cylinders, motors, or actuators. The speed of motion of these devices is a direct function of flow rate – reducing the flow rate reduces the speed of their operation and vice versa.

The different types of hydraulic flow control valves include fixed flow control valves, adjustable flow control valves, throttling flow control valves, and pressure compensated flow control valves. The mechanism for flow control within these valves will vary based on the mechanical design of the valve, which usually is one of the familiar valve styles common to other valves, namely:

Ball
Butterfly
Diaphragm
Needle
Plug
Flow rate can be measured in several different ways, which are not equivalent, so the selection of a flow control valve necessitates understanding what is meant by flow rate. The three common measures of flow rate include:

Volumetric flow rate – measured in units of volume per unit time, such as in3/sec or cc/min.
Weight flow rate – measured in units of a weight per unit time, such as lb/sec.
Mass flow rate – measured in mass per unit time, such as slugs/sec or kg/min.
Some of the common hydraulic flow control valves are:

Pressure-compensated, variable flow valves
Pressure- and temperature-compensated, variable flow valves
Priority valves
Deceleration valves
Pressure-compensated proportional flow-control valves
Proportional flow-control logic valves

Full text

Hydraulic Valves. In this article, we will talk about hydraulic valves used in
irrigation in general.
*Featured
-Controlling pressure and increasing the uniformity of
water distribution
-Remote control by electric, pneumatic or hydraulic
-Protecting pumps,filters and pipelines from
excessive pressure and reducing the effect of water
hammer

)Pressure Reducing (PR) Valve (
It reduces the water pressure after the valve to ensure
a constant pressure in the direction of the water exit,
regardless of the disposal rate or the pressure before
the valveve

)Pressure Sustaining (PS) Valve (
It maintains the pressure before the valve at a fixed
preset level. Some components of the irrigation
system require a certain pressure to function
efficiently, such as the filter washing process, so it is
installed after the filters.

Pressure Reducing & Pressure Sustaining )(PR/PS) Valve (
It combines the properties of the two valves so that
the pressure behind the valve can be fixed while
reducing the pressure leaving it.

)Quick Relief or Safety (QR) Valve (
It works as a safety valve for the network, as it
responds quickly to the increase in network pressure
by releasing the excess pressure by draining the
water into the air when the pressure is increased from
the predetermined value, and
when the pressure drops to the specified value, it
closes slowly to avoid the occurrence of water
hammer and thus preserve the irrigation network from
damage.

)Valve Flow Control (
Restricts flow to a specified flow rate.

)Control ( Valve Level
It closes when the required water level is reached,
and opens when the water level drops below the
predetermined level. It is used in water tanks.

)Hydraulic Check Valve (
The stopcock is closed when the pressure is increased
beyond the pressure value before the stopcock, and it
opens when reversing, and therefore it is used
immediately after the pumps to protect them.