Hydraulic Terms TUV, Hydraulic phrases TUV, Hydraulic glossary TUV

Hydraulic Terms TUV speaks to hydraulic phrases TUV and hydraulic glossary TUV which are words and phrases starting with the letters TUV used in the hydraulic industry.

Tandem Center Valves Using tandem center valves when in a neutral position bypasses the flow of hydraulic oil to the return line. This is used to hold the cylinder/piston in position with no load on the pumps.

When this system is the pump is running constantly to keep a ready supply of hydraulic oil, but as long as the cylinder/piston is not in operation the pump is working under no pressure or load. This system keeps wear and tear on the pump down to a minimum.

Torque Torque is a rotary or turning effort. Torque indicates a force is present at a distance from a motor shaft. One unit for measuring torque is lb inches (newton meter). Torque tells us where a force is in relation to the motor shaft.

Unloading Valve The Unloading valve is installed in systems using accumulators (below). The function of this valve is to "unload" the pump of pressure until such time as a device on the system, such as a cylinder, actually begins operation. In this way, the pump is allowed to operate without load (pressure) until it is needed.

The unloading valve is not intended to replace the pressure relief valve. In fact, the pressure setting of the unloading valve is much lower than the setting on the pressure relief valve.

Hydraulic Terms TUV

Vacuum Gauge A vacuum gauge measures vacuum pressure and is calibrated from 0 to 30 inches of mercury (0 to 760 mm HG). Each division is one inch of mercury.

Vacuum Pressure Scale A vacuum is any pressure less than atmospheric. Vacuum pressure is a source of confusion since the scale begins at atmospheric, just as gauge pressure but works its way down in units of inches of mercury.

Valve It consists of a body and an internal moving part which connects and disconnects passages within the body. The passages in hydraulic valves carry liquid. The action of the moving part controls maximum system pressure, direction of flow and rate of flow.

Valve; Directional Control A valve whose primary function is to direct or prevent flow through selected passages.

Valve; Flow Control A valve whose primary function is to control flow rate

Valve; Flow Dividing A valve which divides the flow from a single source into two or more branches.

Vane Pumps Vane pumps generate a pumping action by causing vanes to track along a ring. The pumping mechanism of a vane pump basically consists of rotor, vanes, ring and a port plate with kidney shaped inlet and outlet ports.

Hydraulic Terms TUV

Vane Pump Double A double vane pump consists of housing with two cartridge assemblies, one or two inlets and two separate inlets and two separate outlets. In other words a double pump consists of two pumps in one housing. This pump can discharge two different flow rates from each outlet. One prime mover is used to drive the whole unit.

Vane Loading Before a vane pump can operate properly, a positive seal must exist between vane tip and cam ring. When a vane pump is started centrifugal force is relied on to throw out the vanes and achieve a seal.

Vane Motors A vane motor is a positive displacement motor which develops an output torque at its shaft by allowing hydraulic pressure to act on vanes which are extended. The rotating group of a vane motor basically consists of vanes, rotor, ring, shaft and a port plate with kidney shaped inlet and outlet ports.

Vapour Pressure and Temperature The vapour pressure of a liquid is affected by temperature. With an increase in temperature more energy is added to the liquids molecules which move more quickly and the vapour pressure increases. When the vapour pressure equals the atmospheric pressure liquid molecules freely enter the atmosphere and is known as boiling.

Variable Orifice Many times a variable orifice is more desirable than a fixed orifice because of its degree of flexibility. Gate valves, globe valves and needle valves are examples of variable orifices.

Variable Volume Vane Pumps In some cases it is desirable that a pump’s flow rate be variable. This can be done by varying the speed of the prime mover.

Velocity Pressure Pressure in a hydraulic system caused by kinetic energy.

Hydraulic Terms TUV

Vent Springs Pilot operated relief valves can be equipped either a high or low vent spring.

Vent Spring Low A low vent spring exerts minimal pressure on the main spool of a pilot operated relief valve. This allows pump flow to return to tank through the valve with the least possible resistance during venting. A low vent spring is the standard main spring of a pilot operated relief valve.

Vent Spring High A high vent spring is a stiffer spring biasing the main spool. It is a greater resistance to tank during venting.

Viscosity A petroleum base hydraulic fluid has two important functions to act as a medium for energy transmission and to lubricate internal moving parts of a system Both of these functions and hydraulic systems in general are influenced by fluid viscosity which is probably one of the most significant characteristics of a petroleum base fluid. Viscosity is the resistance of a liquid’s molecules to flow or slide past each other and is sort of an internal friction.

Viscosity and Clearance Flow It is important that viscosity has the ability to help reduce leakage between clearances of close fitting moving parts.To achieve the best seal possible, clearances between moving parts are kept to a minimum but clearance size is not so small that a fluid cannot pass through and lubricate. Size of a clearance is frequently a compromise between sealing and lubrication.

Viscosity and Heat Generation Viscosity of a petroleum base hydraulic fluid affects heat generation as it along with friction and changing direction was one of the liquids resistance to pump flow. A high viscosity liquid will have more internal resistance to flow and thus more heat will be generated in a system than a low viscosity system.

Hydraulic Terms TUV

Viscosity and Hydrodynamic Lubrication The ability to form a durable fluid film is an important characteristic of petroleum base fluid and is called lubricity. It may be felt that a fluid film would be difficult to maintain between moving parts since any rapid movement would tend to scrape a surface clean. Once parts begin to move, liquid viscosity does not let this happen.

Viscosity Index Since the viscosity of hydraulic oil does change with temperature and since viscosity is an important factor in a hydraulic system, systems which are not, or cannot be, maintained at a constant temperature need an oil whose viscosity remains relatively stable over a given temperature range. The viscosity index is an indication of how viscosity is affected by temperature.

Viscosity and Pressure Viscosity is affected by system pressure. As pressure in a system increases, viscosity increases.

Hydraulic Terms TUV

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