Hydraulic Terms C speaks to hydraulic phrases C and hydraulic glossary C words and phrases used by those involved in the hydraulics industry.
Case Drain All
variable volume pressure compensated pumps must have their housings externally
drained. The pump mechanisms in these pumps move extremely fast when pressure
compensation is required. Any build up of fluid within the housing would
hinder their movement.
Cavitation A circumstance that occurs in pumps when existing space is not filled by available fluid. Cavitation will deteriorate the hydraulic oil and cause erosion of the inlet metal. Cavities form within a fluid because the liquid is made to boil. The boiling in this instance is not caused by heating but is brought about by reaching low absolute pressure. The most noticeable indication of such is noise.
The collapse of cavities causes high amplitude vibrations to be transmitted through the system and a high shrieking sound to emit from the pump. During cavitation there is also a decrease in pump flow rate because the pumping chambers do not completely fill with liquid and system pressure becomes erratic.
Check Valve A check valve basically consists of a body with inlet and outlet ports and a movable member which is biased by spring force. The movable member can be a flapper, or plunger but most often in hydraulic systems it is a ball or poppet. Fluid flow passes through a check valve in one direction only. When system pressure at the check valve inlet is high enough to overcome the spring force biasing the poppet, the poppet is pushed off its seat.
Flow passes through the valve. This is known as the check valve’s free flow direction. When fluid flow enters through the outlet, the poppet is pushed on it’s seat. Flow through the valve is blocked.
Circuit, Open A circuit in which return fluid is directed to the reservoir.
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Circuit; Pilot Used to control a main circuit or component.
Circuit; Regenerative Used to increase cylinder speed by directing rod end discharge to the piston side of the cylinder. Can be incorporated into directional control valve as fourth position.
Closed-Center System A system in which the pump continually operates against a load, even in the neutral condition.
Closed Center Valves This type of valve is used in a hydraulic system where the valve blocks the flow of oil from the pump into an accumulator. The accumulator is used to store the oil under pressure. This valve takes the pressure off the pump and in neutral locks the cylinder in place with no load on the pump.
Contaminant Any material or substance which is unwanted or adversely affects the fluid power system or components, or both.
Control Valves The ways you can harness the power of a hydraulic system is through the use of control valves. The three basic types of control valves are the tandem center type, the open center (motoring spool) type, and the closed center type.
Both the tandem center and the closed center types are available in a three way or four way valve. BY opening or closing valves, you can control how much or in what direction a hydraulic piston moves. Valves can also control many pistons working with each other at the same time.
Control Valve Non-passing A normal non-passing pressure control valve has primary and secondary passages disconnected, and pressure at the bottom of the spool is sensed from the primary port.
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Control Valve Passing A normally passing pressure valve has primary and secondary passages connected and pressure at the bottom of the spool is sensed from the secondary port.
Coolers Coolers remove heat from hydraulic systems as the reservoirs are sometimes incapable of dissipating extra heat.
Counterbalance Valve This is a normally non-passing pressure control valve which can be used to balance or counteract a weight such as the platen of a press.
Cracking Pressure Cracking pressure is the point at which a simple relief valve begins to open a flow path back to the tank. This point is somewhat below the relief valve setting. Simple relief valves have characteristic early cracking pressures.
Crossover Relief Valves A bidirectional motor circuit, using braking relief valves in both directions, can be designed so that the discharge from the relief valves is connected to the opposite motor lines. It may appear that these crossover relief valves would keep the motors inlet well supplied since the motors discharge fluid is redirected to motor inlet.
Cushion A device which provides controlled resistance to motion. They protect against excessive shock a cylinder can be equipped with cushions. Cushions slow down a cylinder’s piston movement just before reaching the end of its stroke.
Cushions can be applied at either ends of a cylinder. A cylinder consists of a needle valve flow control, a cushion spear attached to the cap end side of the piston and a cushion sleeve over the rod. These devices act like plugs at their own respective ends.
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Cylinder A hydraulic actuator constructed of a plunger or piston inside a cylindrical housing. The piston or plunger operates because of pressurized liquid. In all applications hydraulic working energy must be converted to mechanical energy before any useful work can be done. Hydraulic cylinders convert hydraulic working energy into straight line mechanical energy.
Cylinder Cap A cylinder end closure which completely covers the bore area.
Cylinder Capacity, Extending Volume required for one full extension of the cylinder.
Cylinder Capacity, Retracting Volume required by one full retraction of the cylinder. (Generally, less than extending)
Cylinder; Depth Control A mechanical or hydraulic device, adjustable, for limiting cylinder stroke.
Cylinder; Double Acting A cylinder which can apply force and motion in either direction.
Cylinder Force Through the stroke of a cylinder, hydraulic working energy is applied to the area of its movable piston. The pressure component of working energy applied to the piston will be no more than the resistance which a load offers. Cylinder Load Type Cylinders can be used in an unlimited number of applications to move various types of loads.
In general a load which is pushed by a cylinder rod is termed a thrust load. A load which is pulled by a cylinder rod is called a tension load.
Cylinder Mounting Styles Cylinders can be mounted in a variety of ways, among which are flange, trunnion, side lug and side tapped, clevis, tie rod and bolt mounting. Centreline mount would be a very good choice to minimize leakage due to cylinder movement.
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Cylinder; Rephasing A cylinder design which permits the use of two or more cylinders in series, automatically synchronizing cylinder position at the end of each stroke.
Cylinder; Single Acting A cylinder which can apply force in one direction only.
Cylinder Stroke This is the distance through which working energy is applied determines how much work is done. This is the cylinder stroke. It has been illustrated that a cylinder can be used to multiply a force by the action of hydraulic pressure acting on a piston area.
Cylinder Thrust The push of a
cylinder in pounds:
Thrust = Piston Area (in.) x Pump Pressure (PSI) or
Thrust = bore diameter squared x .78 x PSI
Cylinder Volume Each cylinder has a volume or displacement which is calculated by multiplying its stroke in inches by the square inch area of the piston. This will give a volume of so many cubic inches.
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