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Blog - Hydraulic Valve Types

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Hydraulic Valve Types

There are various types of hydraulic valves, some control the hydraulic system pressure in a required level, some valves control fluid flow way to help actuator to achieve its action, other valves are responsible for the actuator operation speed, and some small valves play its important role, like check valves and etc. The hydraulic valves have many categories, although the valve function is four kinds as generally used in industry. –

 (1) Category valve feature and usage:

General hydraulic valve is one of the most common of the three types of hydraulic valve (directional control valve, pressure control valve and flow control valve). The common hydraulic valve is controlled by manual, mechanical, hydraulic, electric, electro-hydraulic, pneumatic, and input control, on or off fluid flow channel, the value control (switched) fluid flow pressure and flow and can be used for general hydraulic drive systems.

A. Directional control valves
Used to control and change fluid flow direction in hydraulic system calls directional control valve, including check valve, prefill valve, hydraulic solenoid directional valve, hydraulic spool directional valves, shut-off valve, etc.

B. Pressure control valves
Used to control and adjust fluid pressure in hydraulic system calls pressure control valve, it includes hydraulic pressure relief valve, pressure reducing valve, pressure sequence valve, pressure switch, etc.

C. Flow control valves
Used to control and adjust fluid flow rate is called flow control valve, and includes throttle valve, speed control valve, pressure relief and flow control valve, manifold set flow valve, etc.

Special hydraulic valve is on the basis of normal hydraulic valves for the further meet certain specific requirements and development. The valve of the structure, use and are not the same.

A. Multi-block directional control valves
Multi-directional valve referred to as spool directional control valves, is combined more than two valve sections as valve main valve, with directional control valve, pressure relief valve and check valve as one multi-function combo valve. The valve centralized controls over more than two of actuator motion, are mainly used for industrial mobile machinery, focus on centralized control.

B. Modular valves
The modular valve is installed by subplate mounting and several valves can be installed together by modular or sandwich, with bolts to achieve different hydraulic circuits.

C. Cartridge valves
This valve has hydraulic control feature of the element as a component screwed into a valve block or manifold, cartridge valve has extend to many sorts of function, such as directional control, pressure relief, flow control function.

D. Electro-hydraulic servo valves
Electro-hydraulic servo valve is called servo valve as well, is to accept electrical analog control signals and output the analog liquid power valve.
The valve is designed for developing valve level of control, control accuracy and response characteristics and focused on valve of the zero point (Typically the input signal is zero from work spot) of performance and its continuity.
Servo valve consists of a single pole, two and 3-pole electro-hydraulic flow servo valve and electro-hydraulic pressure servo valve. Servo valve is structural complexity, manufacturing costs are relatively high, poor anti-pollution capacity, there is a high level of technology requirements and normal maintenance. It is more used in a higher closed-loop control system requires hydraulic accuracy and response control.

E. Electro-hydraulic proportional valves
Electro-hydraulic proportional valve is the valve between the normal hydraulic valve and electro-hydraulic servo valve, this valve can control the hydraulic system fluid flow direction, pressure and flow continuously in a long-distance in accordance with the electrical control signal (analog) and proportional size. It is including electro-hydraulic proportional pressure valves, electro-hydraulic proportional flow control valve, electro-hydraulic proportional directional control valve, electro-hydraulic proportional multi valve and electro-hydraulic proportional multi-directional control valves.
The valve has largely increased the level of hydraulic control stage, in spite of its performance not better than electro-hydraulic servo valve, but it simple structure, lower production costs, stronger anti-pollution make it more popular in industry. The electro-hydraulic proportional valve is mostly used for open or closed-loop system, to maintain the pressure adjustment value of the time stability (Generally for a signal of zero zone corresponds to 10 % ~ 30% maximum control).

F. Electrical-hydraulic digital valves
Electro-hydraulic digital valve is used in digital information to achieve direct control, the valve can be directly connected to computer, does not need to install count/template (D/A) converter. The valve is a more ideal control element in the real-time control of the electro-hydraulic system. There are digital pressure control valve, digital flow control valve and digital directional control valve. Digital valve is not much sensitive to oil contamination, it is also reliable operation, high repeatable precision and good consistency for bulk of product performance.
However, the digital valve controls signal bandwidth lower than analog due to the carrier frequency in accordance with the principles of work. Digital valve flow rate is at a very small, therefore, it can only be used for small flow control applications, such as the electro-hydraulic control valve pilot control level.

G. Micro-hydraulic valves
All hydraulic valve operation port diameter less than 4mm can be called micro-hydraulic valve. The micro hydraulic valve is high working pressure, the maximum working pressure is generally above 31.5 MPa, there are some ones higher than 50 MPa. Micro-hydraulic valve is an important part in micro-hydraulic system, which is new species developed in the based on the normal hydraulic valves. Its outline dimensions and weight largely decreases, therefore, it plays an important role and significance for modern hydraulic machinery and equipment (e.g. aircraft, scientific instruments, medical equipment, etc. ) of small, lightweight and power density increase.

H. Water pressure control valves
Water pressure control valve is the valve to work as water media, which is indispensable water control element in integral water hydraulic system. The water pressure control valve has the characteristics of a safety, health and environment-friendly.
However, the development of water pressure control valve is faced a series of technical challenges due to water main feature of low viscosity, vaporization pressure is high, highly corrosive. There are less commoditized products and the application is not yet universal.

(2) Category by spool function:

A. Sliding spool valves
The valve housing is made of casting iron, there is a cylinder hole through the center of valve house, with several round grooves, each groove connects with inlet or outlet chambers. The valve spool is manufactured a plurality of annular shoulder groove, according its requirement function, it is called shoulder between the valve housing and spool annular groove. Controlling the size of gap between the valve housing and spool, to achieve all of the oil ports on or off and the port diameters, therefore, the valve main job is to control fluid flow direction, pressure and flow control. The spool valve sealed by gap, therefore, the radial clearance between spool outer dimensions and valve housing hole inner dimensions should be as small as possible and keeping appropriate axial seal length, so as to ensure the seal of enclosed ports. When the spool valve starts to open operation ports, the spool needs to move a short distance(equal to the length of the seal ), the area of movement is a “isolated zone”.

B. Rotary valves
The valve spool is cylindrical type, there are inlet and outlet ports on the valve housing and grooves on the valve spool. The spool of valve can be rotated and controls working oil port on or off, to achieve fluid flow direction, pressure and flow control. The structure of rotary valve is sample, but there is a problem of spool radial force imbalance.

C. Poppet valves
Like the spool valve, the poppet valve is most popular in industry. There are two types of valve spool, ball type and poppet type. The poppet valve controls the fluid flow direction, pressure and flow by changing oil port size through poppet and ball spool displacement.
There are only inlet and outlet port of poppet valve, the angle of the poppet is usually design for 12 ° ~ 40 °, better sealing performance since it is line sealing when the valve sets to close, no isolated area while opening, sensitive operation, quickly open fluid flow, its function is similar to spool valve.

D. Nozzle valves
There are single and double nozzle types for the valve. The valve changes the variable throttle gap between nozzle and baffle, alter the relative displacement to control its formed throttle resistance in order to control the pressure at P1 and P2, while changes the size of fluid flow port and spool position. The nozzle valve with the characteristics of high operation accuracy and sensitivity working control, good dynamic response, but it is lots of powers loss, poor pollution, often is used as multi-stage electro-hydraulic control pilot stage (pre-stage ) valve.


  Picture Description:

Pic. A: Sliding spool valve ; Pic. B: Rotary valve;  Pic. C: Poppet valve ; Pic. D: Nozzle valves

1 – Valve housing ;  2 – Valve spool, poppet seat, ball ;  3 – Block ;
4,5 – Nozzle ; 6,7 – Throttle hole ; 8 – Oil reservoir

(3) Category by operation:

A. Manually operated valves
The manual valve is operated by hand, wheel, knob, hand lever, pedals operated, it is applied for less automation requirements, small or infrequent adjustable hydraulic system.

B. Mechanically operated valves
The mechanical valve is controlled by certain block, spring parts, it is suitable for automatically cycle hydraulic system.

C. Electrical operated valves
The electrical operated valve is mostly used as solenoid operated valve, the valve is controlled by many kinds of element, solenoid, proportional solenoid, power motors, torque motors, servo motor and stepper motor control. It is suitable for automation equipment requiring high performance hydraulic system or control of special hydraulic requirements.

D. Hydraulically operated valves
The hydraulically operated valve is controlled by a force generated by hydraulic force. The valve is suitable for high automation hydraulic equipment or special requirements of hydraulic system.

E. Electro-hydraulic valves
The electro-hydraulic valve consists of hydraulic electrical valve and hydraulic control valve, like our valve of FT-WEH series. The valve is most suitable for high automation requirements or customized hydraulic systems.

F. Pneumatic control valves
The pneumatic control valve is operated by the force generated by compressed air. The valve is suitable for flame-retardant and explosion-proof requirements’ hydraulic system.

(4) Category by valve connection and installation:

Hydraulic valves and other hydraulic components are integrated into a complete hydraulic system, the hydraulic unit design depends on the way of valve installation and connection. There are four ways of valve installation connections.

A. Threaded connection valves
The inlet and outlet port of the valve are produced to threaded type, to connect pipe fittings. The structure of threaded valve is sample, light weight, much suitable for mobile equipment and small flow hydraulic systems. The valve is widely used in industry area, but it can be only mounted along pipelines, which may cause more oil leakage spots and inconvenient for hydraulic system maintenance.

B. Modular valves
The modular valve requires valve subplate as a way of connection, the modular valve is mounted on a subplate (there a oil porting pattern on the subplate), the inlet and out ports of the valve connects the pipeline through the valve subplate.hydraulic-valve-types

The manufactures like Finotek company generally provides a related subplate or valve manifolds according to standard porting pattern of modular hydraulic valves. If mounting dimensions of a manifold or subplate manufactures by clients, it can produces according to the size of the valve, the mounting surfaces of various modular hydraulic valves have been standardized nowdays, like CETOP, NFPA, ISO4401, DIN 2430 standards.

If there are several modular hydraulic valve to install on a common manifold, the valve mounting dimensions should be produced based on the requirements of each hydraulic valves installation dimensions and hydraulic system schematics, the valve manifold block needs to drill related connection channels to valve ports and connectors threaded to fit pipes, to form a hydraulic flow loop.
Further standard hydraulic valve can be mounted on the each side of manifold (Each manifold side is like a connection subplate), the oil flows inside the valves and manifold channels to control hydraulic force, the manifold design is be able to save mounting space in hydraulic system and without hydraulic pipes to save the cost.
One or two valve replacement or maintenance on a manifold will not affect the hydraulic system piping installation, therefore, the modular hydraulic valve is extremely easy to manipulate and maintain. Finotek modular hydraulic valve is widely used industry area for its advantage, like in injection modeling machines, pressing machines, hydraulic power units and numerous equipment.

C. Sandwich plate valves
The sandwich plate valve is developed on the basis of modular valve, a more compact structure valve.
A sandwich plate valve can be used as single valve or hydraulic oil connection, the top and bottom surface of sandwich plate valve is installation surface (Often produced as per standard port pattern), used for valve oil port pattern connection. Different functions of the same size valve (like pressure valves, flow valves, directional valves) is manufactured to same valve installation dimensions and oil port pattern, like Z2S6 series, Z2FS series valves.

The valve is sandwiched mounted (Use like a sausage sandwiched in middle of two pieces of bread ) between a directional control valve and subplate or manifold, fastened buy four long bolts as per hydraulic system requirements, the hydraulic system pipe system connects oil ports threaded on the manifolds or subplate.
The hydraulic system with modular hydraulic valve will be able to omit many hydraulic pipes, lower problems of hydraulic resistance, oil leakage, surrounding pollution, working vibration, large noise and often maintenance, to greatly compact and simplified hydraulic system. The valve is widely used industry machines and equipment.

D. Cartridge valves
There are two styles of cartridge valve, cover plate type (two way cartridge valve) and threaded types ( two , three , four-way cartridge valves ). The cartridge valve parts is simple, manufactured as per requirement standard to valve sleeve, spools, seat, spring or sealing rings. All the parts are assembly to a complete cartridge valve, then inserted in cartridge valve cavity, with other different function valve plate and pilot control valve to form various requirements of hydraulic oil circuit.
A manifold allows to install several cartridge valves if needed, the channels inside the manifold comes across each other according to design demand to control hydraulic flow and pressure, the manifold fixed installation and connects pipes in hydraulic system.
The cartridge valve has advantages of compact structure, flow capacity, better sealing and interchangeability. It is suitable for heavy machinery, metallurgy, plastic injection machine and machine requires high-pressure and high flow hydraulic system.