SYSTEM TYPES
Needle valve is a device that has a variable orifice that restricts flow in both directions.
In hydraulic work holding there are two basic types of systems:
1. Coupled or Live 2. De-coupled
The power supply can monitor and compensate for minor system leaks The power supply can help monitor for expansion/contraction due to temperature deviations Clamp/unclamp cycle times are typically reduced by elimination of pressure connection manipulation. More control flexibility for automated systems. / unloading as well as while the functioning operation is being performed. This will offer the following advantages: Coupled or Live systems This type of system remains connected to the power supply during the entire process of loading The disadvantage is that it that there is a limited degree of mobility of the fixture due to the connection to the power supply. In some cases, additional mobility can be achieved by utilizing a rotary union. A rotary union transmits flow through a rotary coupling thus allowing rotation of the fixture under pressure. In other applications, hose guides or a through pallet coupling to the machine may also be used, to add mobility to the fixture.
One of the major drawbacks to this type of valve is that due to the area differential of most double acting devices, there is a potential to create damaging pressure spikes in the system if the valve gets totally closed. Another drawback to this type of valve is that, as it will restrict fluid flow in both directions, potentially affecting the return performance of single acting devices being returned by spring force alone. Because of these potential drawbacks, Vektek no longer offers a needle valve.
Flow control valve is a device that combines the function of a needle valve with that of check valve.
This allows restricted flow in one direction and free or unrestricted flow in the other direction. To prevent the potential of creating pressure intensification in a hydraulic power clamping system, in most cases, it is recommended that the flow control valve be installed in such a way that the flow is metered into the device. Metering in is typically referred to as speed control, while metering out is typically referred to as load control, which has the potential to cause pressure spikes. Additional information about metering for speed / load control can be found in other publications such as “Fluid Power Directory” and “Industrial Fluid Power”
Hydraulic Clamping Fundamentals Aug 09 Rev - D
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