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Hydraulic Valves

Hydraulic valves are parts that control the flow and pressure of hydraulic fluid within a system. They allow hydraulic equipment to function properly and safely while allowing for precise control. Hydraulic valves are made up of a main casing, which is the outer enclosure that holds all the other components. The other components are a bonnet, or a removable section of the casing, a seat, which is the interior surface where the connection is made, and a disc that acts as the seal that prevents leaking at the seat.

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Since 1912, Fulflo Specialties has been providing "chatter free" products that modulate to regulate pressure. The company is able to provide customers with an extensive line of parts, which can mount in any position. A pioneer in fluid power, we constantly strive to be a worldwide product producer leader. For all hydraulic valves and other pressure needs, contact Fulflo.
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For over sixty years, The Lee Company has been an industry leader when it comes to manufacturing high quality miniature hydraulic valves for use in aerospace systems, oil tools and other industries worldwide. They offer a wide selection of products to provide customers with the solutions they need. For questions or quotes contact The Lee Company for your next order.
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Industry Information

View A Video on Hydraulic Valves- A Quick Introduction

Hydraulics valves are varied in terms of how they operate and what they do when functioning. For example, electric hydraulic valves are computer controlled and do not require an operator because they can be remotely controlled and operated. Hydraulic solenoid valves are also electrically operated devices. Hydraulic proportional valves are called proportional because the output flow is not equal to the input flow. Hydraulic manifolds are composed of a variety of hydraulic valves that are connected to each other within the hydraulic system. The shape of hydraulic valves also affects performance and usage. Hydraulic needle valves have small ports with thin threaded plungers that allow for tight flow regulation in hydraulic systems. Hydraulic ball valves are used in critical high pressure applications that require a quick and easy shutoff because the handle is manually rotated 90° between the open and close positions. Other common hydraulic valves include cartridge valves, check valves, directional control valves, control valves and relief valves. The size of hydraulic valves can range from less than an inch to a foot long; the average valve can fit in the palm of a hand. Common materials include brass, bronze, copper, cast iron and stainless steel as well as plastics such as PVC.

Basic hydraulic valves have two stations: open and closed. When closed, no fluid is able to pass through but when open, it flows freely. Hydraulic valves are used within a fluid control system as a simple way to prevent improper levels of pressure and fluid. They are used with hydraulic tools or equipment such as water cutting machines or backhoes. Hydraulic valves are predominately used in equipment and tools founds in industrial, manufacturing or construction applications and are found in the aerospace, automobile, military, food processing, process control, oil or fuel, wastewater, irrigation, gas or air, steam, fire service, cryogenic, refrigeration, chemical and laboratory or medical industries. Which type of hydraulic valve is used in what type of industry completely depends on what each individual valve is intentionally produced to do. For example, electric hydraulic valves are found in underground piping and fluid control systems because they are a simple way to manage pressure and fluid levels. Though the flow rates are low, needle valves provide a steady and precise flow of fluid and are therefore used for calibration or flow regulating applications.

Some valves shut off flow when flow rates get too high, while others transmit signals to other valves in order to provide a systematic balance of flow. These valves protect hydraulic systems from being exposed to high pressures that exceed the mechanism's specified limits. The solenoid converts electrical energy into mechanical energy. When the wire coil receives a current, a magnetic field acts upon the plunger, which results in opening or closing of the valve. Hydraulic check valves have two openings: an inlet in which the fluid enters and an outlet through which the fluid exits. They prevent backflow. Hydraulic directional control valves permit flow in more than one direction because they have a component that shifts or rotates to line up with the corresponding pipes or tubes and accommodate a number of ports. Hydraulic control valves prevent improper levels of pressure and fluid in hydraulic systems. Hydraulic relief valves are used to limit the pressure in a hydraulic system by allowing the pressurized hydraulic fluid to flow out of the system into an auxiliary passage. Protecting the passage of the substance as well as the environment through which it is passing is the overall goal of hydraulic valves, as well as protecting the substance and its source.

Hydraulic valves have an important place within everyday life. Without the ability to control the flow rate and pressure of fluids within a hydraulic system, many processes would become unsafe and ineffective. Hydraulic lines have existed for many years but were not initially utilized for many applications. Rather, they were kept in science labs and inventors tinkered with them. In modern times, however, hydraulic lines are widely used, making hydraulic valves very important. Innovations have resulted in a variety of valves that enable complex movements and precise control over fluids. The development and production of electronically controlled hydraulic valves has led to heavy duty equipment capable of lifting large loads as well as complex systems of tubes and lines leading to actuators that perform important manufacturing processes. Valves are even now used in vehicles to control the flow of fluids. These devices can be smaller than the tip of a pencil which is especially useful for environments where space is at a premium. The shrinking size of valves allows them to be used in places where they could not have fit before. When they are added to these hydraulic systems, the lines become safe and more effectively controlled. They are also available in large sizes to fit lines with big diameters, offering the same benefits.


hydraulic valve
Image Provided by Fulflo Specialties, Inc.



Hydraulic Valves Types

  • Ball valves are parts that control the flow and pressure of a fluid by using a spherical element to create a seal. Ball valves are used in critical high pressure applications that require a quick and easy shutoff.
  • Cartridge valves are completely bodiless and can be removed and replaced easily without dismantling.
  • Check valves are hydraulic valves which allow flow in only one direction. Any backflow forces the valve to shut.
  • Control valves are used to contain and transfer the flow and pressure of hydraulic fluid in hydraulic systems. There are many different designs of hydraulic control valves, including check, cartridge, directional, relief, safety, shut off, and solenoid valves. Hydraulic control valves come in a variety of sizes and pressure ratings.
  • Conventional safety relief valves (CSRV) are a type of spring-loaded pressure relief valve. The characteristics of this valve are directly affected by changes to backpressure within the valve.
  • Directional control valves control the direction of the hydraulic fluid to the point where it is needed. Directional control valves are useful for hydraulic tools and farm equipment that use hydraulics. 
  • Electric valves valves are parts that are able to control the flow and pressure of fluid when an electric signal triggers them to open or close.
  • Float valves are valves that automatically open or close as the liquid level changes. Float valves are operated mechanically by a float that rests on top of the liquid.
  • Gate valves are linear motion valves in which a flat closure element slides into the flow stream to provide shut-off. Gate valves are designed to minimize pressure drop in fully open positions.
  • Globe valves are multi-turn valves that have a closing element that moves perpendicular to the valve body seat and generally seals in a plane parallel to the direction of flow. This type of valve is suited both for throttling and general flow control.
  • Hydraulic valves are parts that control the flow and pressure of hydraulic fluid within a system. The main parts include a casing, a bonnet, a seat and a disc.
  • Manifolds are devices that regulate fluid flow between components in a hydraulic system. They let an operator know how much fluid is flowing between the pump and actuators, the hydraulic devices that move or control a mechanism.
  • Needle valves have small ports with thin threaded plungers that allow for tight flow regulation in hydraulic systems. Though the flow rates are low, needle valves provide a steady and precise flow of fluid and are therefore used for calibration or flow regulating applications.
  • Pressure safety valves (PSV) are actuated by inlet pressure and re made to rapidly open or close. They feature a tight shut-off and are used for safety purposes only.
  • Pressure relief valves (PRV) are utilized to re-close and prevent any further flow once normal conditions are re-established.
  • Proportional valves are parts that manage fluid flow and pressure within a hydraulic system. They are called proportional because the output flow is not equal to the input flow.
  • Relief valves (RV) are made to release pressure. When safe pressure levels are exceeded, the valve opens and then closes when levels are back to safe presets.
  • Safety relief valves (SRV) are a type of pressure relief valve that are easily identified by their rapid opening and closing, which is directly proportional to increases in pressure.
  • Solenoid valves are made from wire coil and a movable plunger that is set against the coil. Solenoid valves are electromechanical devices that use solenoid to control the valve's actuation.



Hydraulic Valve Terms

Accumulator - A container that stores fluid under pressure and is used to absorb hydraulic shock.
 
Backpressure - The pressure exerted on the downstream side of a valve seat.
 
Bonnet - A removable outer piece of a valve that makes assembly possible, sometimes considered part of the body.
 
Bleed - A small controlled line of fluid from a pressurized system.
 
Cavitation - When gas enters into the liquid stream and causes the pressure to reduce to the vapor pressure. 

Cracking pressure -  This occurs when the valve begins to leak flow, prior to the set pressure.

Cylinder - A device that is used to convert hydraulic energy to mechanical motion and force.

Differential Set Pressure - The pressure differential between the set pressure and constant superimposed backpressure.
 
Disc - The o-ring or metal wedge that seals the valve to the seat.
 
Full Flow - A condition in which the maximum amount of fluid must be allowed to travel through the system.
 
Flow Rate - The volume, mass or weight of fluid passing through a flow passage, regulated by valves.
 
Gear Boxes - Used to ensure easier operation of larger valves, particularly ball valves.
 
Hydraulic Actuator - A device fitted to the valve stem that uses hydraulic energy to open and close the valve.
 
Hydraulics - The study of fluids in motion.
 
Meter - Used to measure pressure level and volume of fluid in a hydraulic system.
 
Overpressure - The pressure increase or accumulation above the set pressure when the valve is discharging flow.
 
Pre-Charge - The residual pressure in a hydraulic actuator before the introduction of oil.
 
Reduced Bore - Indicates that the internal diameter of the valve is lower than the piping to which the valve is fitted.
 
Seal - A device that restricts the escape of fluid or entrance of foreign material.
 

Seat - The fixed surface on which a valve rests or against which it presses. 

Set pressure - This occurs when the inlet pressure of the valve is adjusted to one of three settings: open, maintain, or control.

Solenoid - A coil of wire designed to carry an electrical current producing a magnetic field.
 
Superimposed Backpressure - The static pressure existing at the outlet of the relief device at the time the device is required to operate. It is a result of the pressure in the discharge system coming from another source. May be constant or variable.
 
Static Water Pressure - The measured pressure of water when it is not moving.
 
Viscosity - A measure of the internal friction or resistance of a fluid to flow. Viscosity is determined by measuring the liquid shear strength under specific conditions.




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