Hydraulic valves are used to direct and control the flow of fluids through a system of pipes, hoses, or cylinders, converting the fluid force into mechanical energy. This energy is transmitted through the hydraulic system by a series of accumulators, pumps and actuators to operate a wide range of equipment for a vast array of functions. They are generally part of a "closed loop" system with a reservoir, that allows the fluid to expend its driving force before being returned to the reservoir for continuous function.
Uses for Hydraulic Valves
Hydraulic valves are used in cars to actuate brakes, clutches, and gears. They are used in engine lubrication and air conditioning systems. Some car jacks use hydraulic cylinders to provide lift. The Jaws of Life utilize a system of hydraulic piston rods that can cut, spread, push, or pull a vehicle apart to rescue passengers.
Some hydraulic valves can handle several thousands of pounds per square inch of pressure and are found in heavy equipment operation. They control dump beds on trucks, swing arms on backhoes, blade adjustments on graders, track drives, conveyors, scissor lifts, and forklifts. Hydraulic valves are found in all industrial timber cutting and processing equipment, water and sewage treatment facilities, power plants, mining operations, oil, gas, and petroleum works, food harvesting, processing, and packaging operations, chemical processing plants, and plastics manufacturing.
Hydraulic control valves can be used to operate tiny nano-bots that perform microsurgery with masterful precision as easily as they control crane booms that can lift railroad cars or place construction materials on catwalks hundreds of feet in the air. They are at the heart of manufacturing automation and robotics. Without hydraulic components, there would be no amusement parks or draw bridges, and many industries would be reduced to a crippling crawl.
Hydraulic Valves Suppliers – The Lee Company
Hydraulic Valves Suppliers – The Lee Company
Hydraulic Valves Distributors – Fulflo Specialties, Inc.
Hydraulic Valves Distributors – The Lee Company
Hydraulic Valves Suppliers – Fulflo Specialties, Inc.
Hydraulic Valves Suppliers – Fulflo Specialties, Inc.
A Brief History of Hydraulic Development
In Ancient Greece, Aristotle noted that water is a continuum. A century later, Archimedes
stated that a body in water floats due to the force of displacement and
that pressure gradient is an essential part of flow. Leonardo DaVinci
developed the first mathematical flow formula at the turn of the
sixteenth century, and designed the first known closed loop control
system to regulate the flow rate of water to a water wheel.
All of these grounding theories were pertinent to the
advancement of hydrostatics (water at rest) and hydrodynamics (water in
motion), paving the way for hydraulic (water powered) developments.
In 1648, Frenchman Blaise Pascal presented the Hydrostatic
Transmission Theory claiming that pressure applied to a static fluid is
transmitted equally in all directions. Now known as Pascal's Law, this
theory is the fundamental basis of hydraulics.
Joseph Bramah patented the first hydraulic machine in 1795.
It was an industrial press with designs still in use. His progress was
followed by the likes of Robert Boyle, Sir Isaac Newton, Daniel
Bernoulli, and Leonhard Euler, all of whom lent their knowledge to the
field of hydraulics.
Around 1907, Harvey Williams and Reynolds Janney developed
the first axial piston devices, which were both pumps and motors, that
used the fluid medium as a lubricant. Water was not an adequate medium,
so oil hydraulics came into existence, nearly obliterating the water
In 1956, a misplaced mining wagon ruptured a hydraulic oil
line and severed an electrical line at a mine in Belgium. The ensuing
fire killed 262 people, inciting new legislation that required mines and
manufacturers to use water hydraulics for safety reasons. These systems
are still considered a safe, effective alternative to oil hydraulics.
Both systems are in use today.
How Hydraulic Valves Are Made
Most hydraulic valves are made from iron, brass, steel, or
stainless steel. Smaller units may be made from plastics. The seat, or
outer housing of a valve, and the body, or inner component that opens
and closes the channel, may be cast, die forged, or machined. An
external wheel or lever is incorporated with the body to operate it.
How Hydraulic Valves Work
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. The
simplest hydraulic valve uses two equally sized pistons in two cylinders
connected by a pipe filled with hydraulic fluid. When force is applied
to one piston, the other rises. Because the fluid can not be made
smaller, it is considered incompressible, and may only be displaced.
This means that the pipe containing the hydraulic fluid may be any size,
shape, or configuration. As long as it is full and no compressible air
bubbles are present, pressure applied at one end will result in
virtually equal force at the other end.
Hydraulic power transmission is very effective. It may be
divided through the use of a manifold and subsequent slave cylinders
that are operated by a master cylinder. The most prevalent example of
this is the braking system on an automobile. One pedal operates the
brakes on all four wheels at the same time.
The force at the business end of a hydraulic valve may
be "stepped up" or "stepped down" by changing the size of one piston and
cylinder in a process of hydraulic multiplication or division. For
example: a two inch diameter cylinder with a nine inch long piston will
raise another two inch diameter piston nine inches with an applied force
of one hundred pounds.
If the second piston has a diameter of six inches, it has a
surface area nine times larger than the two inch piston. The smaller
piston will only move the larger piston one inch in distance, but the
resulting force is multiplied by nine, providing nine hundred pounds of
pressure from one hundred pounds of initial force. Mathematical formulas
may be applied to calculate accurate valve sizes and configurations for
any hydraulic system.
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.
Types of Hydraulic Valves
The type of hydraulic
control valve placed in the system will depend on the specifications of
the job. Some valves such as ball valves, butterfly valves, globe
valves, check valves, and gate valves are simple flow control valves
that are generally either fully open or completely shut.
- 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.
- 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 hydraulic 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
- 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 hydraulic 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
- 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.
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
- 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.
- A spool valve,
also known as a directional valve or directional control valve, is used
as a switching device to control hydraulic equipment. It blocks and
opens fluid pathways inside the valve to activate power transmission. It
is a cylinder with a cutaway view resembling a thread spool, sealed
inside a casing. Valves on one side lead to a pump and storage tank.
Other valves may lead to a single device, or to a hydraulic manifold
which directs power to multiple devices. The controller moves the spool
into different positions, moving the fluid through the system. Pressure
flows either from the pump to the devices or from the devices back into
the fluid reservoir, but only provides force in one direction, depending
on the position of the spool, which determines whether the force pushes
- A proportioning valve,
or p valve, regulates the output pressure in a system with multiple
hydraulic lines. Commonly found as components of braking systems for
cars, p valves provide less pressure to rear brakes to keep them from
- A solenoid valve,
or s valve, is an electromechanical valve. An electrical current is run
through a coil which creates a magnetic field. This causes a plunger to
open or close the valve. Solenoid valves may be direct-acting, in which
case the plunger opens and closes an internal orifice directly, or they
may be pilot-operated, also known as servo-type valves, wherein the
plunger operates a pilot orifice. Fluid pressure in the line passing
through the pilot orifice operates the valve seal. Most s valves have an
inlet port and an outlet port, classifying them as two port valves,
although they may be designed with more outlet ports. Because they are
controlled with electricity, they can be computer programmed to operate
- Hydraulic Cartridge valves, also
known as logic valves and 2/2 valves, are threaded inserts that screw
into a cavity in a manifold or a valve body. They may be used to control
flow rate, direction, or pressure.
- Check valves
are directional control valves that only allow hydraulic fluids to flow
one way. They are two port valves, meaning they have one inlet and one
outlet, that are opened by the pressure of the fluid flow within, and
shut by any backpressure that flows back into the pipe.
- Relief valves
are types of safety valves designed to release pressure once it has
built to a specific point. In equipment operation, hydraulic relief
valves will relieve pressure by sending excess hydraulic fluid back to
the storage tank. These valves may be pressure activated or spring
loaded. Commonly found on water heaters, a safety relief valve will vent
steam if the water in the tank gets too hot.
- Position Valves,
or 3-way valves, consist of two valves in a single body with a shared
input and exhaust port. They are used as pilot control for hydraulic
- 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
Hydraulics In Motion
One of the simplest hydraulic devices is the log splitter.
It is driven by an engine, typically a four-stroke gas motor, attached
to an oil pump. The pump pushes the oil into a spool valve that operates
a ram. The spool valve moves fluid into the ram with "stepped up"
force. The ram of the log splitter is a hydraulic cylinder, with a wedge
at the head, which splits the wood as the operator applies pressure to
the lever. A reservoir contains the hydraulic oil. It is often equipped
with a filter to maintain the cleanliness of the oil.
A gear pump is the most common type of pump found in
hydraulic systems. It is a positive displacement pump and is used to
move high-viscosity fluids continuously. The gears are housed inside the
pump casing and are classified as external or internal depending on the
configuration. Gear pumps use two spur gears that mesh together. One of
the gears is driven by a motor, the other, called an idler, is driven
by the first gear. The counter-rotation creates a void in the intake
side, suctioning hydraulic fluid into the rotation and moving it out the
exhaust port. Tight tolerances between gears prevent backflow.
The ram is a piston rod that is driven by the fluid being
pumped through the spool valve. In the log splitter, the pump pushes oil
against the ram, which applies increasing pressure to the log, until it
splits. The lever is released, the oil returns to the accumulator, and
the process may begin again.
In heavy equipment, series of pumps and rams are
inter-connected through hydraulic lines to perform heavy duty moving,
lifting, digging, and farming. These same tools on a miniaturized scale
can be trusted to perform delicate brain or eye surgery. The valves that
operate multiple component systems can be computer controlled for
accuracy and automation.
Hydraulic Maintenance and Safety
Wear gloves and safety glasses. Hydraulic fluids often contain
chemicals that can irritate skin and eyes. A pinhole leak in the system
can spray oil at very high pressure, injecting the oil into the skin.
Accidental ingestion can cause grave illness.
- Monitor temperatures. Most hydraulic fluids are flammable.
- Clean up spills. Hydraulic fluid is a lubricant. It will lubricate the floor as readily as equipment.
out for the environment. Conventional hydraulic oil is not
environmentally friendly. There are options available that are. If
alternatives don't work for specific applications, make sure to handle
the fluids responsibly.
the pros handle it. They can ensure machines are operating properly.
They can offer information and tips on better performance or
maintenance. They can fix existing problems, spot potential issues, and
prevent future breakdowns.
Hydraulic Valve Terms
container that stores fluid under pressure and is used to absorb hydraulic
– The pressure exerted
on the downstream side of a valve seat.
– A removable outer piece of
a valve that makes assembly possible, sometimes considered part of the body.
– A small controlled line of
fluid from a pressurized system.
– 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.
– A device that is used to
convert hydraulic energy to mechanical motion and force.
– The pressure
differential between the set pressure and constant superimposed backpressure.
– The o-ring or metal wedge that
seals the valve to the seat.
– A condition in which the
maximum amount of fluid must be allowed to travel through the system.
– The volume, mass or weight
of fluid passing through a flow passage, regulated by valves.
– Used to ensure easier
operation of larger valves, particularly ball valves.
– A device fitted
to the valve stem that uses hydraulic energy to open and close the valve.
– The study of fluids in
– Used to measure pressure level
and volume of fluid in a hydraulic system.
– The pressure increase
or accumulation above the set pressure when the valve is discharging flow.
– The residual pressure
in a hydraulic actuator before the introduction of oil.
– Indicates that the internal
diameter of the valve is lower than the piping to which the valve is fitted.
A device that restricts the
escape of fluid or entrance of foreign material. –
– 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.
– A coil of wire designed
to carry an electrical current producing a magnetic field.
– 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.
– The measured
pressure of water when it is not moving.
– 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.
Hydraulic Valve Informational Video