Hydraulic Pumps

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 pumps¡¯ 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.

Control Valves

Control valves or proportional valves are power-operated devices used to modify fluid flow or pressure rate in a process system. These valves are used throughout industry in many applications. Control valves types include globe, diaphragm, pinch, knife or gate, needle, butterfly, ball, and plug. Globe valves are linear motion valves with rounded bodies, from which their name is derived. They are widely used in industry to regulate fluid flow in both on/off and throttling service. Diaphragm valves are related to pinch valves, but use an elastomeric diaphragm, instead of an elastomeric liner in the valve body, to separate the flow stream from the closure element. Instead of pinching the liner closed to provide shut-off, the diaphragm is pushed into contact with the bottom of the valve body to provide shut-off. Pinch valves includes any valve with a flexible elastomer body that can be pinched closed, cutting off flow, using a mechanism or fluid pressure. Pinch valves are full bore, linear action valves so they can be used in both an off/on manner or in a variable position or throttling service. Gate or knife valves are linear motion valves in which a flat closure element slides into the flow stream to provide shut-off. Gate control valves are usually divided into two types: parallel and wedge-shaped. The parallel gate valve uses a flat disc gate between two parallel seats, upstream and downstream. Knife valves are of this type, but with a sharp edge on the bottom of the gate to shear entrained solids or separate slurries. Needle control valves have a slender, tapered point at the end of the valve stem that is lowered through the seat to restrict or block flow. Fluid flowing through the valve turns 90 degrees and passes through an orifice that is the seat for a rod with a cone shaped tip. Butterfly valves are quick opening valves that consist of a metal circular disc or vane with its pivot axes at right angles to the direction of flow in the pipe, which when rotated on a shaft, seals against seats in the valve body. They are normally used as throttling valves to control flow. Ball valves provide tight shut-off and characterizable control. They have high rangeability due to the design of the regulating element, without the complications of side loads typical of butterfly or globe valves. Plug control valves, also called cock or stop-cock valves, date back to ancient times, where they were developed for use in citywide Roman plumbing systems. Today, they remain one of the most widely used valves for both on/off and throttling services.
Important specifications to consider when searching for power-operated control valves include diameter, working pressure, and operating temperature. Media types include gases, liquids, and liquids with suspended solids. The material temperature is also important to consider. Metal material choices for valve body include brass, bronze, copper, cast iron, ductile iron, Monel, stainless steel and steel. Plastic material choices include PVC and CPVC. There are many choices for end configuration on control valves. These include threaded, socket-weld or buttweld, push on, solder end, clamp, grooved end, flangeless wafer-style, lugged, mechanical joint, and flanged. Valve actuation methods for control valves include electric, pneumatic, hydraulic, and manual. Seat features include metal-to-metal, o-ring or soft seat, Class IV or V, and Class VI. Control valves may configure to ANSI standards, API standards, MSS specifications, UL listings, ASME standards, and Federal specification WW-V-35C. Check with manufacturer for exact listings. Some control valves may come configured as a multi-piece design. Common applications for control valves include general purpose, process control, oil or fuel, sanitary, wastewater, water, irrigation, gas or air, steam, fire service, cryogenic, refrigeration, chemicals, and laboratory or medical.

 

Pressure Control Valves

Pressure control valves are designed to provide protection from over-pressure in steam, gas, air and liquid lines. control valves and back pressure regulators are the same device, only differing in application. The pressure control valve "lets off steam" when safe pressures are exceeded, then closes again when pressure drops to a preset level. A back pressure regulator maintains upstream pressure at the desired setting by opening to allow excess upstream pressure to flow downstream.
Pressure control valves are self-operating valve that is installed in a process system to protect against over pressurization of the system. control valves are designed to continuously regulate fluid flow, and to keep pressure from exceeding a preset value. There are a wide variety of valve designs, but most resemble diaphragm valves, globe valves, or swing check valves. With many of these designs, a helical or hydraulic pressure spring is used to maintain a constant force acting on the backside of the valve disk or diaphragm, causing the valve to be normally closed. When the force exerted by the process stream (i.e. fluid pressure) on the valve disk is greater than the constant force exerted by the spring, the valve opens allowing process fluid to exit the valve until the fluid pressure falls below the preset value. These valves can be preset to a specific control pressure or they may be adjustable.
The flow transfer and control category covers a wide spectrum of products designed to facilitate, control, maintain, meter, or read the flow of material through hoses, pipes or tubing. The material in question can be liquid, gaseous, or semi-solid (colloids and slurries). The following families fall within this category: valves, valve actuators and positioners, dispensing valves, pumps, flow sensing, level sensing, density and specific gravity sensing, viscosity sensing, and miscellaneous related products.
Valves are apparatus designed to maintain, restrict, or meter the flow of materials through pipes, hoses, tubing or entire systems. They generally function by allowing flow while in their open position, and restricting flow when closed. The valve family is broken down into product areas based on the mechanism that is used to restrict flow. The following are the main valve product area: ball valves, butterfly valves, check valves, diaphragm valves, gate or knife valves, globe valves, needle valves, pinch valves (for both industrial and medical applications), plug valves, control valves (1/4 turn - isolation and multi-turn, throttling), pressure control valves, and AC and DC solenoid valves.

Hydraulic Valves

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¡ã 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.

Hydraulic Cylinders

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 Power Units

Hydraulic power units provide pressurized flow to hydraulic motors, cylinders, and other hydraulic components. Hydraulic power units (HPUs) differ from pumps, as an HPU contains a fluid reservoir, multiple pump stages and coolers to keep fluid at a safe working temperature. Performance specifications, physical characteristics, and features are all important parameters to consider when searching for hydraulic power units.
Performance specifications to consider when selecting hydraulic power units include operating pressure, flow, total power, and reservoir capacity. The operating pressure is the pressure the power unit can deliver at the outlet. The power unit may be expressed as a single pressure rating, or it can be rated to operate over a range of pressure. The fluid flow through the power unit may be a single rating, or have low and high rating points. The total amount of power the motor / pump can draw or is rated to operate. Some power units have multiple power sources, and this specification is the power available from all sources. Power is measured in horsepower, or similar units. The capacity of the power unit reservoir is measured in gallons or similar units. Some units may have interchangeable or modular reservoirs with a range of capacities.
Physical specifications to consider for hydraulic power units include the pump type, power source, cooling method, and unit weight. All hydraulic power units have some type of integrated pump. Some units are available with multi-stage pumps, which perform like multiple pumps connected in series. Pump types available for hydraulic power units include single stage, double stage, three or more pump stages, and multiple pump units. Power sources include electric motor, diesel engine, gasoline engine, and pneumatic compressor. The cooling method can be none, heat exchanger, or fan-driven oil cooler. The unit weight is also important to consider.