HYDRAULIC CYLINDERS HYDRAULIC TERMS
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Set screw - Uses two recessed set screws. The letters UC indicate set screws. Shuttle Valve - Used primarily to control pilot flows. This valve has two inlets and one outlet. The flow with the highest pressure is accepted and the other is blocked. Both flows are kept separate. The floating poppet is free to move back and forth, closing the inlet with the lowest pressure. Used with very low-pressure systems. Single-Acting Cylinder - A cylinder will have the capacity to be utilized in only one direction. Commonly referred to as “power up, gravity down”. The extend or push phase is controlled by a valve, but the retract or return phase is achieved by the weight of the application. A dump body is a prime example. Solenoid - An electro-magnetic device which positions a hydraulic valve. Spherical Bearing - A spherical bearing is a bearing that accommodates some misalignment of one or both pivot pins. It
is a bearing that is pressed in to a tang and is located at the rod end, base end or both. Spring Return to Neutral - The handle springs back to the neutral position when released. Starvation - A lack of oil in vital areas of a system. Often caused by plugged filters, etc. Static - Stationary or fixed
Static Pressure - The pressure in a fluid at rest. (A form of “potential energy.”) Static Seal - This is a seal that does not move. It’s not dynamic, it’s static. Steel Shields - A bearing number is followed by the suffix ZZ indicates that the bearing is sealed on both sides by steel shields. Strainer - A coarse filter. Stroke - The distance which the piston travels through the cylinder tube between the gland and the base plate. Since the rod is attached to the piston, this is the usable travel or movement of the cylinder. Stroke Controls - These controls are used to limit the stroke of a hydraulic cylinder. There are several variations of this idea. Stroke control segments can be added to the rod to limit the return stroke. Some stroke limiters are installed inside the cylinder tube to control the extension or the outward stroke. Sub-plate - A method for mounting a single solenoid valve. Suction Pressure - The absolute pressure of the fluid at the inlet side of the pump. Surge - A momentary rise of pressure in a hydraulic circuit. Surge Pressure - The pressure changes caused in a circuit from a rapidly accelerated column of oil. The “surge” includes the span of these changes, from high to low. Switch - a mechanical, electrical, electronic, or optical device for opening or closing a circuit or for diverting energy from one part of a circuit to another. Such as a remote control or solenoid switch. System - One or more series of component parts connected to each other. Often made up of two or more “circuits”. System Pressure - The pressure which overcomes the total resistances in a system. It includes all losses as well as useful work. T Tandem Center Valve - A valve, in which the inlet and outlet ports or connected in the neutral position, allowing flow back to tank, while the work ports are blocked. Tang - A single protrusion from the base plate and/or the rod of a cylinder, drilled and centered to allow for mounting on an application. This male end fits inside a clevis-type mounting and is pinned. TEFC - Totally enclosed fan cooled (electric motor frame style) Telescopic Cylinder - Consist of two or more “stages”. Each stage extends the cylinder to its maximum and then another stage extends and so on until the complete cylinder is extended. Telescopic cylinders can either be single or double acting. Telescopic cylinders are used in applications where the retracted length needs to be shorter than half of the extended length. Terminal Expansion - Expansion of the fluid volume due to heat.
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