Today, buyers are demanding quiet machines because of their concern about meeting industry’s noise limits. Vickers is helping to meet this demand by supplying quiet hydraulic components. Sound levels of some pumps today, for example, are fifty percent lower than the same model pumps of a few years ago.
Sound Advice
Producing quiet, hydraulically-actuated machines requires more than just the use of quiet components.
Meeting the stringent sound-level specifications of today’s industrial hydraulic systems and machines takes careful engineering. The pump should be considered first. It not only produces sound directly but generates vibrations and fluid pulsations. These react with other machine parts which produce more sound.
Pump Selection
Pumps generate more acoustic energy per unit of hydraulic power by running at high speed rather than at low. For this reason, a pump should operate at 1200 RPM whenever sound is critical. Below 3000 PSI, the trade-off between pressure and pump size for a given drive power has little effect on noise, so you are free to select any combination of these factors that otherwise meet your needs.
Mechanical Isolation
To meet lower sound level limits, the pump should be mechanically isolated from the rest of the machine using anti-vibration mountings. This also requires that all connections to the pumps be made with flexible hose.
Flexible hose will often reduce noise even where anti-vibration mountings are not used. It prevents vibrations from reaching other lines and components to keep them from becoming sound sources. In long lengths, this hose is, itself, a good sound generator so only short lengths should be used. For long runs, use solid pipes with short hoses at the ends. All long lines must be supported every meter or so, preferably with clamps providing vibration damping. Lines must not contact panels that are good sounding boards. Where they pass through such panels, allow sufficient clearance to prevent direct contact; never use bulkhead fittings in such cases.
Acoustic Isolation
The greatest sound level reductions are attained with the pump acoustically as well as mechanically isolated. This requires that the pump be completely enclosed in a non-porous shell weighing at least 10 kg per square meter of surface. No openings can be tolerated and all joints must be sealed with resilient gaskets or moldings.
Grommets of rubber or other soft material should be used to close openings around piping and to prevent mechanical contact between the enclosure and piping. It must be emphasized that while mechanical isolation by itself can reduce noise, acoustic isolation can only be effective when used in combination with mechanical isolation.
Fluids
The condition of the fluid being pumped is also important in controlling sound. Fluid viscosity, temperature and vacuum by themselves have no effect on sound levels. It is important to control them, however, to prevent the formation of entrained air or vapour bubbles that can double sound levels, and reduce pump life.
A combination of high fluid temperature and inlet vacuum generates what are called cavitation bubbles. However, at low temperatures, a high viscosity fluid in a very long suction line can also produce sufficient vacuum to cause cavitation. Important methods of suppressing bubble formation include: Using short runs or large diameter inlet lines; keeping the reservoir elevation close to or above that of the pump; using low pressure-drop inlet filters that signal when they are producing high vacuums and need changing; and, providing adequate fluid controls. These are all good hydraulic practices that become increasingly important where you must achieve low sound levels.
Reservoirs
Reservoirs provide the means for releasing entrained bubbles. These can come from sources other than the pump inlet and are usually present in the fluid returning to the reservoir. It is important to note that low reservoir temperatures reduce the rate of bubble escape and may result in incomplete release. As pointed out earlier, high temperatures promote bubble formation. The best balance between these two alternatives is achieved by maintaining the temperature of oil leaving the reservoir in the range of 120o to 150oF and the temperature of water-based fluids between 100o and 120oF.
A simple reservoir has to be large to effect complete bubble release. By providing baffles to guide the fluid through a circuitous path and by locating return and pump inlet lines as far apart as possible, a reservoir holding between two to three minutes of maximum pump flow can be adequate.
Sound Advice
Producing quiet, hydraulically-actuated machines requires more than just the use of quiet components.
Meeting the stringent sound-level specifications of today’s industrial hydraulic systems and machines takes careful engineering. The pump should be considered first. It not only produces sound directly but generates vibrations and fluid pulsations. These react with other machine parts which produce more sound.
Pump Selection
Pumps generate more acoustic energy per unit of hydraulic power by running at high speed rather than at low. For this reason, a pump should operate at 1200 RPM whenever sound is critical. Below 3000 PSI, the trade-off between pressure and pump size for a given drive power has little effect on noise, so you are free to select any combination of these factors that otherwise meet your needs.
Mechanical Isolation
To meet lower sound level limits, the pump should be mechanically isolated from the rest of the machine using anti-vibration mountings. This also requires that all connections to the pumps be made with flexible hose.
Flexible hose will often reduce noise even where anti-vibration mountings are not used. It prevents vibrations from reaching other lines and components to keep them from becoming sound sources. In long lengths, this hose is, itself, a good sound generator so only short lengths should be used. For long runs, use solid pipes with short hoses at the ends. All long lines must be supported every meter or so, preferably with clamps providing vibration damping. Lines must not contact panels that are good sounding boards. Where they pass through such panels, allow sufficient clearance to prevent direct contact; never use bulkhead fittings in such cases.
Acoustic Isolation
The greatest sound level reductions are attained with the pump acoustically as well as mechanically isolated. This requires that the pump be completely enclosed in a non-porous shell weighing at least 10 kg per square meter of surface. No openings can be tolerated and all joints must be sealed with resilient gaskets or moldings.
Grommets of rubber or other soft material should be used to close openings around piping and to prevent mechanical contact between the enclosure and piping. It must be emphasized that while mechanical isolation by itself can reduce noise, acoustic isolation can only be effective when used in combination with mechanical isolation.
Fluids
The condition of the fluid being pumped is also important in controlling sound. Fluid viscosity, temperature and vacuum by themselves have no effect on sound levels. It is important to control them, however, to prevent the formation of entrained air or vapour bubbles that can double sound levels, and reduce pump life.
A combination of high fluid temperature and inlet vacuum generates what are called cavitation bubbles. However, at low temperatures, a high viscosity fluid in a very long suction line can also produce sufficient vacuum to cause cavitation. Important methods of suppressing bubble formation include: Using short runs or large diameter inlet lines; keeping the reservoir elevation close to or above that of the pump; using low pressure-drop inlet filters that signal when they are producing high vacuums and need changing; and, providing adequate fluid controls. These are all good hydraulic practices that become increasingly important where you must achieve low sound levels.
Reservoirs
Reservoirs provide the means for releasing entrained bubbles. These can come from sources other than the pump inlet and are usually present in the fluid returning to the reservoir. It is important to note that low reservoir temperatures reduce the rate of bubble escape and may result in incomplete release. As pointed out earlier, high temperatures promote bubble formation. The best balance between these two alternatives is achieved by maintaining the temperature of oil leaving the reservoir in the range of 120o to 150oF and the temperature of water-based fluids between 100o and 120oF.
A simple reservoir has to be large to effect complete bubble release. By providing baffles to guide the fluid through a circuitous path and by locating return and pump inlet lines as far apart as possible, a reservoir holding between two to three minutes of maximum pump flow can be adequate.
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