Hydraulic cylinders are actuation devices that utilize pressurized hydraulic fluid to produce linear motion and force. Hydraulic cylinders are used in a variety of power transfer applications. Operating specifications, configuration or mounting, materials of construction, and features are all important parameters to consider when searching for hydraulic cylinders.

Important operating specifications for hydraulic cylinders include the cylinder type, stroke, maximum operating pressure, bore diameter, and rod diameter. Choices for cylinder type include tie-rod, welded, and ram. A tie-rod cylinder is a hydraulic cylinder that uses one or more tie-rods to provide additional stability. Tie-rods are typically installed on the outside diameter of the cylinder housing. In many applications, the cylinder tie-rod bears the majority of the applied load. A welded cylinder is a smooth hydraulic cylinder that uses a heavy-duty welded cylinder housing to provide stability. A ram cylinder is a type of hydraulic cylinder that acts as a ram. A hydraulic ram is a device in which the cross-sectional area of the piston rod is more than one-half the cross-sectional area of the moving component. Hydraulic rams are primarily used to push rather than pull, and are most commonly used in high pressure applications. Stroke is the distance that the piston travels through the cylinder. Hydraulic cylinders can have a variety of stroke lengths, from fractions of an inch to many feet. The maximum operating pressure is the maximum working pressure the cylinder can sustain. The bore diameter refers to the diameter at the cylinder bore. The rod diameter refers to the diameter of the rod or piston used in the cylinder.

Choices for cylinder configuration are simple configuration or telescopic figuration. A simple configuration hydraulic cylinder consists of a single cylindrical housing and internal components. A telescopic configuration hydraulic cylinder uses “telescoping” cylindrical housings to extend the length of the cylinder. Telescopic configuration cylinders are used in a variety of applications that require the use of a long cylinder in a space-constrained environment. Hydraulic cylinders can be single action or double action. A single action hydraulic cylinder is pressurized for motion in only one direction. A double action hydraulic cylinder can move along the horizontal (x-axis) plane, the vertical (y-axis) plane or along any other plane of motion. Choices for mounting method include flange, trunnion, threaded, clevis or eye, and foot. The mount location can be cap, head, or intermediate. Materials of construction include steel, stainless steel, and aluminum. Common features for hydraulic cylinders include integral sensors, double end rod, electro-hydraulic cylinders, and adjustable stroke.

Hydraulic pumps deliver high-pressure fluid flow to the pump outlet. Hydraulic pumps are powered by mechanical energy sources to pressurize fluid. A hydraulic pump, when powered by pressurized fluid, can rotate in a reverse direction and act as a motor. Operating specifications, housing materials, and features are all important specifications to consider when searching for hydraulic pumps.

Pump type and pump stages are the most important operating specifications to consider when searching for hydraulic pumps. Choices for hydraulic pumps types include axial piston, radial piston, internal gear, external gear, and vane. An axial piston pump uses an axially-mounted piston to pressurize fluid. Mechanical motion from the pump’s power source moves the piston through a chamber, pressurizing the fluid it comes in contact with. A radial piston pump uses pistons mounted radially about a central axis to pressurize fluid. An alternate-form radial piston motor uses multiple interconnected pistons, usually in a star pattern. The hydraulic pump’s power source causes the pistons to move, forcing the pistons through the chambers and pressurizing fluid. An internal gear pump uses internal gears to pressurize fluid. The pump’s power source causes the internal gears to turn, which forces fluid through the pump outlet. An external gear pump uses external gears to pressurize fluid. The pump’s power source causes external gears to turn, which forces fluid through the pump outlet. A vane pump uses a vane to pressurize fluid. The pump’s power source causes the vane to rotate. As the vane rotates, blades on the vane push fluid out the pump’s outlet. Pump stages include single stage, double stage, triple stage, and four or more pump stages.

Additional operating specifications to consider for hydraulic pumps include continuous operating pressure, maximum operating pressure, operating speed, operating horsepower, operating temperature, maximum fluid flow, maximum fluid viscosity, displacement per revolution, and pump weight. The continuous operating pressure is the maximum pressure available at the pump outlet. The maximum operating pressure refers to the maximum peak pressure available at the pump outlet on a noncontiguous (intermittent) basis. The operating speed is the speed at which the pump’s moving parts rotate is expressed in revolutions per minute, or similar terms. The operating horsepower is the amount of power the pump is capable of delivering. Horsepower is dependent on the pressure and flow of the fluid through the pump. The operating temperature is the fluid temperature range the pump can accommodate. Maximum and minimum fluid temperature is dependent upon internal component materials, and varies greatly between manufacturers. The maximum volumetric flow through the pump is expressed in terms of gallons per minute, or similar units. The maximum fluid viscosity the hydraulic pump can accommodate is a measure of the fluid’s resistance to shear, and is measured in centipoise. Centipoise is a common metric unit of dynamic viscosity equal to 0.01 poise or 1 millipascal second. The dynamic viscosity of water at 20 degrees C is about 1 centipoise. The correct unit is cP, but cPs and cPo are sometimes used. The fluid volume displaced per revolution of the pump is measured in cubic centimeters (cc) per revolution, or similar units. The weight of the hydraulic pump is measured in pounds or similar units.

Hand pumps and foot pumps are manually operated pumps that can driven by hand or foot via a handle or lever. This manual external force actuates an internal mechanism, which increases pressure for moving fluids such as gas, chemicals, or water. Hand lever and foot pedals are pushed up or down to begin the pump cycle, often requiring one stroke to draw the fluid and another stroke to discharge it, as is typical in many displacement pumps.

Hand pumps and foot pumps are generally of hydraulic and pneumatic design. Hydraulic hand pumps and foot pumps are used to manually pressurize a hydraulic system and for instrument calibration. Pneumatic hand pumps and foot pumps are designed for testing and instrument calibration. A fluid reservoir is generally supplied with hydraulic and pneumatic hand pumps as an integral part of the pump or an independent part. It holds a quantity of fluid for the pump to use to power hydraulic or pneumatic cylinders.

Hand pumps and foot pumps may also be called drum pumps, which will require handles, levers, and plungers to begin dispensing the fluid from a pail, drum, or tank. Drum pumps may mount manually or with a clamp. Although the actual hand pumps may be portable and lighter in weight, it may be preferable to keep the pail, drum or barrel stationary due to the properties of the fluid and the pumping environment.

Hand pumps and foot pumps can be of reciprocating or rotary types. Most rotary types use a drive rather than a lever or crank. In reciprocating type hand pumps, a hydraulic or pneumatic piston is used to create the pressure needed to move the media. Hand pumps can also be diaphragm pumps as in marine applications where seawater is pumped from the bilge. Diaphragm hand pumps are displacement pumps that use a rubber disk to alternate air or fluid. The diaphragm is actuated by the pressures or vacuums created during the pump cycle.

Hand pumps and foot pumps are portable and field operable where electric drives may not be available. A gage is often attached to hand pumps to measure pressure. Calibration hand pumps can be sold as a kit or will require calibration instruments, indicators, gages, and other instrumentation.

Hydraulic motors are powered by pressurized hydraulic fluid and transfer rotational kinetic energy to mechanical devices. Hydraulic motors, when powered by a mechanical source, can rotate in reverse direction and act as a pump. Operating specifications and features are the most important parameters to consider when searching for hydraulic motors.

The most important operating specification to consider when searching for hydraulic motors is the motor type. Choices for motor type include axial piston, radial piston, internal gear, external gear, and vane. An axial piston motor uses an axially-mounted piston to generate mechanical energy. High pressure flow into the motor forces the piston to move in the chamber, generating output torque. A radial piston hydraulic motor uses pistons mounted radially about a central axis to generate energy. An alternate-form radial piston motor uses multiple interconnected pistons, usually in a star pattern, to generate energy. Oil supply enters the piston chambers, moving each individual piston and generating torque. Multiple pistons increase the displacement per revolution through the motor, increasing the output torque. An internal gear motor uses internal gears to produce mechanical energy. Pressurized fluid turns the internal gears, producing output torque. An external gear motor uses externally-mounted gears to produce mechanical energy. Pressurized fluid forces the external gears to turn, producing output torque. A vane motor uses a vane to generate mechanical energy. Pressurized fluid strikes the blades in the vane, causing it to rotate and produce output torque.

Additional operating specifications to consider for hydraulic motors include operating torque, operating pressure, operating speed, operating temperature, power, maximum fluid flow, maximum fluid viscosity, displacement per revolution, and motor weight. The operating torque is the torque the motor is capable of delivering. Operating torque depends directly on the pressure of the working fluid delivered to the motor. The operating pressure is the pressure of the working fluid delivered to the hydraulic motor. Working fluid is pressurized by an outside source before it is delivered to the motor. Working pressure affects operating torque, speed, flow and horsepower of the motor. The operating speed is the speed at which the hydraulic motors’ moving parts rotate. Operating speed is expressed in revolutions per minute, or similar terms. The operating temperature is the fluid temperature range the motor can accommodate. Minimum and maximum operating temperatures are dependent on motor internal component materials, and can vary greatly between products. The power the motor is capable of delivering is dependent on the pressure and flow of the fluid through the motor. The maximum volumetric flow through the motor is expressed in terms of gallons per minute, or similar units. The maximum fluid viscosity the motor can accommodate is a measure of the fluid’s resistance to shear, and is measured in centipoise. Centipoise is a common metric unit of dynamic viscosity equal to 0.01 poise or 1 millipascal second. The dynamic viscosity of water at 20 degrees C is about 1 centipoise. The correct unit is cP, but cPs and cPo are sometimes used. The fluid volume displaced per revolution of the motor is measured in cubic centimeters (cc) per revolution, or similar units. The weight of the motor is measured in pounds or similar units.

Additional features to consider when searching for hydraulic motors include mounting in any position, rated for continuous duty, and quiet operation.

Hydraulic valves contain and transfer the flow and pressure of hydraulic fluid in hydraulic power systems. They range from simple shutoff valves to precision control valves. Common types of hydraulic valves include angle, ball, block and bleed, check, control, cartridge, directional, drain, needle, poppet, pressure relief, safety, shut off, solenoid, spool, and stack mounted valves. In their unpowered state, hydraulic valves can be normally open (open center) or normally closed (closed center). Hydraulic valves with a tandem center connect the pressure and tank ports, but block the service ports to allow system unloading and isolation of the service lines. Devices with a float center allow the supply to be shut off and enable the load to move to other services.

There are many types of hydraulic valves. Angle valves admit media at an angle and permit maximum flow. Ball valves provide tight shut-off and reliable control. Block and bleed valves use a small port to depressurize the space between the inlet and outlet. Check valves prevent flow reversal. Control valves modify fluid flow. Directional valves steer process media through selected passages. Drain valves are used to remove surplus fluid from a system or container. Needle valves have a slender, tapered point at the end of a valve stem. Poppet valves open and close ports with a sealing device that includes a disk, cone, or sphere. Pressure relief valves remove excess upstream pressure. By contrast, regulators maintain a constant outlet pressure. Safety valves contain a thermal sensing component that opens or closes in response to temperature changes. Spool valves are actuated by a rotary or piston-like spool that slides back and forth to cover and uncover ports in the housing. Shut off valves close a line to stop flow when a pre-set condition occurs. Stack mounted, sandwich, or modular valves can be assembled to create a valve block.

Performance specifications for hydraulic valves include valve size, pressure rating, ports, media temperature, flow coefficient, and connection type. Valve sizes are typically measured in inches (in) while pressure ratings are usually measured in pounds per square inch (psi). Both double-port and multi-port hydraulic valves are available. Media temperature is a maximum amount expressed in degrees Fahrenheit. The flow coefficient equals the number of gallons of 60° F water that flow through a valve at a specified opening with a pressure drop of 1 psi across the valve. There are several connection types for hydraulic valves. Some devices have internal or external threads for inlet or outlet connections. Others use a bolt flange, clamp flange, union connection, tube fitting, butt weld, or socket weld. With compression fittings, tightening a nut on one fitting compresses a washer around the other. With metal face seals, a gasket is sandwiched between two fittings.