Return-Suction Filters – New Catalog Series for In-line Mounting
Particularly in self-propelled machines such as wheel loaders, pavers or mowers which are equipped with a hydrostatic drive (closed circuit) and combined working hydraulic system (open circuit), the filter concept furthermore often consists of a return filter (working hydraulics) and a suction or pressure filter (hydrostatic drive).
At the above mentioned machines, return-suction filters replace the required suction or pressure filters for the feed pump of the closed hydrostatic drive and the return filter for the working hydraulics in the open circuit. Compared to these filter concepts, often also a cost reduction can be achieved.
The use of a return-suction filter offers far-reaching functional improvements and for example, the following advantages:
- Only one filter for both circuits
- In both circuits, the total oil volume is filtered in the return line
- Continuously more oil is flowing in the return line than it is taken off via the suction line
- Excellent cold start behavior, since the feed pump sucks oil which is pressurized by a check valve
- The feed pump is always supplied with filtered oil. A pressure relief valve isinstalled to protect the shaft seals against overloading
The hydraulic oil returning from the circuit (R) passes the filter element (1), is pressurized by a 0.5 bar check valve (2) and supplied to the feed pump (S). The surplus oil flows filtered over the integral check valve into the reservoir (T). As the feed pump is always fed with pressurized oil, the risk of cavitation is minimized and full performance is available even during the critical cold start phase.
An integral bypass valve (3) in the filter element (1) prevents too high back pressure (e.g. with cold start or contaminated filter element).
A bypass valve protection strainer guarantees that – under no circumstances - unfiltered oil can get into the feedpump.
While with the use of separate filters, both circuits operate independently from each other, the combination of the two circuits via a return-suction filter causes interaction between the circuits. If the design criteria described below are taken into account, you can take full advantage of the benefits provided by the return-suction filter concept.
Required return flow in the system
In order to maintain a pre-charging pressure of approx. 0.5 bar at the intake of the feed pump, the return flow must exceed the suction flow under any operating condition.
Permitted flow rate of the feed pump
- At operating temperature and rated speed, the volume flow of the filling pump should not exceed 80% of the nominal volume flow rate of the filter (e.g. with a return-suction filter with a nominal volume flow / return flow of 200 l/min, the volume flow of the filling pump should not be higher than 160 l/min).
- At extreme cold starts (ν = 1000 mm²/s) and slightly increased idle speed
(n = 1000 min-1), the volume flow of the filling pump should be ≤ 80% of the return flow.
Pressure loss in the suction lines
Under above mentioned cold start conditions, the pressure loss in the suction lines must not exceed 0.4 bar. This ensures that the filling pump is supplied with sufficient oil even with a partly contaminated filter element.
Backpressures in system return lines
When the drain oil from the hydrostatic drive is routed across the filter, the permitted leakage oil pressures have to be observed in order to protect the shaft seals. Here, besides the backpressure of the filter, also the pressure loss caused by the leakage oil pipes and the oil cooler are to be considered.
Depending on the application, the use of a cooler bypass valve is recommended.
Filter fineness and oil cleanliness grades
As standard, for all return-suction filters two ARGO-HYTOS filter grades are available: 10EX2 and 16EX2. Both with the patented EXAPOR®MAX2 design. The following oil cleanliness according to ISO 4406 can be achieved:
- 10EX2: 18/15/11 … 14/11/7
- 16EX2 20/17/12 … 17/14/10
The manufacturers of hydrostatic drives mostly recommend for normal operation an oil cleanliness of 20/18/15 and as of 19/17/14 for increased requirements (t > 90 °C). Even with the filter fineness 16EX2 these requirements are met by 100%.
So far, return-suction filters have only been offered as tank top mounting version. As particularly with compact machines the tank often is difficult to achieve, ARGO-HYTOS as only manufacturer to date has developed return-suction filters for in-line mounting. These in-line mounting versions can be integrated in a readily accessible place in the return line and suction line.
|E 068 / E 088||E 178 / E 258|
|Nominal flow||up to 100 l/min, two length variants||up to 250 l/min, two length variants|
|Filter fineness||10EX2 and 16EX2||10EX2 and 16EX2|
|Operating pressure, max.||10 bar||10 bar|
|Bypass valve cracking pressure||2.5 bar||2.5 bar|
|Bypass valve protection strainer||mesh size 125 μm||mesh size 200 μm|
|Return connections||G ¾ (1x)||G1 (4x)|
|Suction connections||G ¾ (1x)||G1 (3x)|
|Tank connection||G ¾||G1|
|Clogging indicator ports||M12x1.5 (plugged) (2x)|
M12x1.5 (plugged) (2x)