Suction return line filters: hydrostatic drive protection

Why a suction return line filter ensures the service life of hydrostatic drives

In modern mobile hydraulics, engineers face the challenge of achieving maximum system availability in the tightest of spaces. As a specialist in hydraulic filtration, RT-Filtertechnik offers a precisely tailored range of suction filters, return line filters, suction return line filters and inline filters. A highly efficient suction return line filter combines two essential filtration functions directly within the hydraulic tank, safeguarding the sensitive feed pump when a hydrostatic drive operates in a closed circuit. A stable pressure range of up to 10 bar ensures reliable filtration, even under extreme mechanical stress.

Traditional filter systems separate the suction and return flow, which takes up valuable installation space. Integrating the functions into a single 2-in-1 housing significantly reduces the system weight, minimises the number of pipes, and simplifies the tank design while maximising full-flow filtration efficiency.

Reliable reduction in cavitation risk

A hydrostatic drive requires a continuous, bubble-free oil supply to the filling pump. Using a suction return line filter to reduce the risk of cavitation helps protect the drive system from long-term abrasive wear. A counterbalance valve integrated into the filter housing maintains the filtered return oil at a constant slight pressure of 0.5 bar as standard. This ensures that the charge pump's suction performance is thermodynamically optimised, and the formation of harmful vapour bubbles in the fluid (cavitation) is reliably prevented, even during sudden load changes.

Prevent cold start problems in mobile hydraulics

Low ambient temperatures as cold as -30 °C can cause hydraulic oil to become highly viscous during winter operation or after extended periods of inactivity, resulting in critical pressure losses in the suction system. To prevent serious cold start problems in mobile hydraulics and ensure the reliable operation of the suction line filter for the feed pump, a pre-charge pressure of 0.5 bar is applied directly to the suction line. Additionally, when dealing with viscous media, the integrated bypass valve (with an opening pressure ranging from 2.5 bar to 3.0 bar, depending on the series) opens to protect the filter element.

A highly efficient anticavitation valve (0.04 bar) with an optional protective screen ensures that oil can be directly drawn from the tank in the event of a temporary oil shortage in the return line, such as during rapid cylinder movements. Dry running the charge pump is therefore physically impossible.

Contamination control and ease of maintenance

The tank-mounted filter's service-friendly design ensures optimal flow performance, with a flow direction from the inside out that can handle pressures up to 10 bar. The medium flows into the element from the inside and exits it once clean.

The key advantage in day-to-day engineering: During element replacement from above, the deposited contamination particles remain entirely inside the closed filter base element and do not return to the tank. This ensures that our range of hydraulic filters is environmentally friendly and easy to maintain, without any compromises. This design also allows powerful magnetic cores to be directly integrated into the cover, enabling highly effective magnetic pre-filtration of even the finest metal particles before they reach the main filter medium. An integrated oil management system ensures highly efficient air separation within the fluid circuit at the same time.

Intelligent valve technology & standards-compliant validation

Specific requirements in the system designs for complex machines often necessitate temperature-dependent control of fluid flow to optimise efficiency. The SRC 3-4 series solves this problem by using a suction return line filter with a thermovalve, which allows for an integrated connection to an oil cooler. Until the hydraulic oil reaches its optimal operating temperature, the valve directs the cold oil flow past the cooler and straight to the filter. Only when the specified temperature is reached does the valve switch precisely, directing the medium through the external cooler and significantly shortening the machine's warm-up phase.

The mechanical stability and filtration performance of glass fibre filter elements (from 5 µm(c)) have been thoroughly validated and quality-controlled across the entire pressure range up to 10 bar, in compliance with international standards: ISO 2941, ISO 2942, ISO 2943, ISO 3968, ISO 11170, and ISO 16889. The robust housing consists of an aluminum cast filter head and a durable steel filter bowl, and is designed to withstand a nominal pressure of 10 bar as standard. It can be equipped with visual or electrical clogging indicators (back pressure switches) as standard for precise maintenance alerts.

Series specifically tailored to your system

For a precise design in the stable pressure range up to 10 bar, you have access to perfectly coordinated series that ensure optimal tank installation. Select your specifications for direct system integration in engineering and purchasing:

Series	Max. flow rate	Max. operating pressure	Max. element removal height	Max. weight with element	Key features & integration
SRA 3-4	230 l/min	10 bar	500 mm	7.1 kg	Compact protection against return flows, with an element that can be removed from the top - ideal for tight spaces.
SRA 3-4	230 l/min	10 bar	550 mm	7.4 kg	Compact protection against return flows, with an element that can be removed from the top - ideal for tight spaces.
SRA 6	420 l/min	10 bar	600 mm	14.9 kg	An advanced performance level for increased flow rates in heavy-duty construction machines. An overpressure of 0.5 bar reduces the risk of cavitation.
SRC 3-4	260 l/min	10 bar	450 mm	6.2 kg	Intelligent thermal management with integrated cooler oil control system (thermovalve) optimises efficiency.
SRC 3-4	260 l/min	10 bar	550 mm	6.4 kg	Intelligent thermal management with integrated cooler oil control system (thermovalve) optimises efficiency.