Suction filters are integrated into the hydraulic system upstream of the pump and are mainly used to protect the pump from impurities from within the system. In this way, they ensure that the system functions optimally and extend the service life of the pump. Contamination may occur during system installation and/or due to the use of contaminated oil during initial filling or subsequent refilling of the system.
Tank-mounted suction filters
Suction filters, which are installed inside the tank, are also known as suction strainers. They are mounted at the end of the suction line, usually via a thread fitting. The suction filter can either be screwed into the line horizontally or vertically. They must be matched to the existing flow rate and system characteristics. However, the suction filter must also be large enough to prevent any cavitation at the pump.
Suction filters are available in different sizes from G 3/8" to G 4", including variants with an NPT thread, and with varying degrees of filter fineness. The most common filter medium for tank-mounted suction filters is metal mesh (wire mesh) with a fineness of 60 µm, 125 µm or 250 µm. Suction filters are available with or (more commonly) without a bypass valve.
When installing a suction filter, it is important to make sure it is placed in the correct position in the tank. When the system is in operation, the suction filter must not be above the oil level, otherwise there is a risk of air being drawn in. However, if the suction filter sits too deep in the tank, debris may be sucked in from the bottom of the tank. Both would lead to cavitation and damage to the pump – and even failure of the entire hydraulic system.
Suction filters outside the tank
Suction filters installed outside the tank are classed as in-line filters. These suction filters consist of a filter head with or without an integrated bypass valve and are installed in the hydraulic line. Their biggest advantage over the strainer variant, which is located inside the tank, is that there is no need to open the tank when replacing the element, thus eliminating the risk of additional dirt entering the system.
In addition, the choice of available filter elements is much larger, allowing more precise integration into the hydraulic system. As a rule, cellulose or glass-fiber elements with a filter fineness of 10–20 µm are used. Depending on the application, filter elements with a 60 µm, 125 µm and 250 µm wire mesh may also be used. A vacuum indicator or vacuum switch signals when the spin-on filter has reached its maximum dirt-holding capacity and needs to be changed.
As with the suction filter in the reservoir, the chosen filter must be matched to the flow rate and system characteristics. When installing a suction filter, pay attention to the flow direction arrow on the filter head. The spin-on must point downwards. It is not possible to install a suction filter in a vertical line. When installing a suction filter, make sure that there is enough space to change the spin-on filter and service indicator. The suction filter should be installed in a location where it can be easily reached in the event of a fault. This will also save time and money when replacing the filter elements.
Suction filters at ELSÄSSER Filtertechnik
Our suction filters are suitable for all HH, HL, HM, and HV-type fluids as standard. The use of other fluids may also be possible subject to prior testing. The operating temperature range is -20°C to +100°C.
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