4 Types of Hydraulic Valves & Their Working Principles
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There are many types of hydraulic valves available in the industry. Hydraulic valves are mechanical equipment for controlling the flow of fluid in hydraulic pipes or systems. They can be utilized to thoroughly check the flow level to a specific domain, redirect pressurized fluid or close a line.
Types of Hydraulic Valves
Hydraulic valves are available in various characteristics similar to other valves, such as bypass, needle, regulating, relief, ball, butterfly, pilot-operated, check, diverter, proportional, and directional. In general, these hydraulic valves may be described as being of three main varieties which are:
Hydraulic Flow Control Valves
Hydraulic Pressure Control Valves
Hydraulic Directional Control Valves
Hydraulic Flow Control Valves
Hydraulic flow control valves are used to regulate the flow volume of passing fluid in hydraulic systems. These types of valves have a movable gate that changes the flow domain to modify the flow rate in the valve. For example, this type of hydraulic valve would be used in control circuits for devices, such as actuators, cylinders, or motors. The speed of these devices is a function of flow rate linearly, i.e. decreasing the flow rate reduces their driving speed and vice versa.
The different types of hydraulic flow control valves are movable flow control valves, pressure compensated flow control valves, fixed flow control valves, and throttling flow control valves. The method of flow control in these valves are modifying based on the mechanical shape of the valve, which regularly is one of the well-known styles same as other valves, namely:
Ball
Butterfly
Diaphragm
Needle
Plug
We can measure flow rate in many distinct ways, which are not similar, so choosing a flow control valve demands understanding what is expected by flow rate. The three standard types of flow rate are:
Mass flow rate – we measure the mass per unit time in the units such as the kg/min or slugs/sec.
Weight flow rate – we measure weight per unit time in the units such as lb/sec.
Volumetric flow rate – we measure volume per unit time in the units such as the cc/min or in3/sec.
Some of the conventional hydraulic flow control valves are:
Pressure-compensated proportional flow-control valves
Deceleration valves
Proportional flow-control logic valves
Pressure- and temperature-compensated, variable flow valves
Pressure-compensated, variable flow valves
Priority valves
Hydraulic Pressure Control Valves
Hydraulic pressure control valves are used to regulate the fluid pressure passing through hydraulic arrangements to keep that pressure at desired amount as restricted by the system operator. Fluid systems are typically produced for operation at a fixed range of pressures. These valves serve a crucial role in preventing rises in pressure that may result in hydraulic fluid leaks or the bursting of pipes and tubes. They are also installed to have the desired pressure in some sections of a hydraulic circuit.
Several kinds of pressure control valves are widespread in hydraulic systems, including reducing valves, relief valves, sequence valves, counterbalance valves, and unloading valves.
Hydraulic Directional Control Valves
We use hydraulic directional control valves to track fluid in a system or circuit to several devices as demanded. They shift between discrete positions such as extend, retract, or neutral locations for controlling a hydraulic cylinder. They can also change into intermediate states to control an actuator’s acceleration, speed or direction.
Discrete hydraulic Directional control valves are a simple form of binary valves, passing blocking the fluid flow. If fluid tries to pass in the reverse direction, a check valve seals the system using a ball, plunger or poppet.
Hydraulic directional control valves with more complicated characteristics may have multiple gates, as their characteristics allow them to switch fluid within distinct ports depending on the device they supply with hydraulic fluid. Consequently, they are discriminated against by standardized numbering systems that have two values, the same as 4/3 or 2/2. The first number indicates the number of valve ports, and the second number indicates the number of valve positions that the device can achieve.
https://www.csiequipt.com/product-hydraulic-system-valves.htmlAccording to this coding scheme, 2/2 represents a two-state valve and 4/3 a four-state valve with three positions. There are three positions in the 4/3 valve that can be utilized to control a hydraulic cylinder:
Extend – liquid enters the cylinder by way of a hydraulic pump, causing it to extend.
Retract – liquid is introduced from the hydraulic pump to the rod end of the cylinder, which in turn causes it to retract.
Neutral – all liquid ports are blocked, so there is no flow of liquid.
Here we list some of the classes for directional-control valves. You can identify these valves according to the:
The number of flow ways in the extreme positions.
The number of spool positions.
Method of providing spool return.
Method of shifting a spool.
Flow pattern in the crossover or center position.
Hydraulic Four-Way Valves
Four-way directional-control valves are installed to manage the direction of fluid flow in a hydraulic line, which commands the direction of the rotation of a fluid motor or the movement of a working cylinder. These valves usually are the sliding-spool model. Standard four-way directional-control valves have four ports:
The exit or return port is attached to a reservoir.
The pressure line is connected to a pressure port.
Two operating ports are connected to an actuating unit.
Four-way valves have a rectangular cast frame, a sliding spool and a way to locate a spool. A spool is a precision fitted to a bore by the longitudinal axis of a body. The lands of a spool partition this bore into a set of separate chambers. Ports in a valve’s body lead into a section so that a spool’s situation determines which ports are open and which ones are closed. Ports that are sealed off from others in one position may be interconnected in different positions. Spool positioning is completed mechanically, electrically, manually, or hydraulically.
The figure below shows how the spool location determines the possible flow states in the line. The four ports are labeled as P, T, A, and B: P is connected to the flow reservoir; T to the tank; and A and B to the ports of the working hydraulic motor, cylinder, or some other valve in the path. In figure A, the spool is in a position that port P is free to port A, and port B is free to port T. Ports A and B are joined to the ports of the cylinder, flowing through port P, and make the piston of the cylinder to travel to the right. Return flow from the cylinder moves through ports B and T. In figure B, port P is free to port B, and the piston travels to the left. Return flow from the cylinder reaches ports A and T.
The table below is presented all Types of hydraulic valves.
Classification
Description
Control type
Manual operated
The hand lever shifts the spool.
Pilot operated
Hydraulic pressure shifts the spool.
Solenoid operated
Solenoid action shifts the spool.
Solenoid controlled, pilot operated
Solenoid action shifts the integral pilot spool and directs the pilot flow to move the main spool.
Path of flow type
Two way
Allows two possible flow paths in two spool positions
Four-way
Allows four possible flow paths in two spool positions
Position type
Two-position
The spool has two positions of dwell.
Three-position
The spool has two positions plus one center or intermediate position.
Spool type
Open center
include five of the common spool types.
Close center
Partially closed center
Semi-open center
Tandem center
Spring type
Spring offset
Spring action automatically turns the spool to the normal offset position when shifter force is released. (Spring offset is always a type of the two-way valve)
No spring
The spool is not spring-loaded; it is moved only by force, and it remains where it is moved (two- or three-position type, however, the three-position type uses detent).
Spring centered
Spring action automatically turns the spool to the center position with releasing force. (Spring-centered is a type three-position valve.)