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Tag Archive: Rexroth

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Variable pumps are a permanent fixture in hydraulics. They develop maximum potential in electrohydraulic design with digital control unit. This is because they then provide the exact flow rate or power required for the respective movement task.

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Hydraulic motor case flushing

Hydraulic motor case flushing

Hydraulic motor case temperature

At the latest my project I used hydraulic motor Rexroth A2FLM710 (710cc). The motor works at 1400 rpm and provides 590 HP to the consumer. For safe motor work, I always try to keep the case temperature below 80*C. The easiest way to do this is a flushing flow adjustment.

In addition to the flow, you need to keep your eyes on the motor case pressure and try balancing to prevent overpressure in the motor case (check in the motor manufacturer’s catalog the max available case pressure to make longer life of motor shaft seals).

The values I have gotten: 21 GPM at 30 psi case pressure and in the worst-case scenario (max motor load, warm hydraulic oil) max case temperature was around 80*C

Hydraulic motor case flushing

Hydraulic motor case flushing flow and case pressure

There are no prescriptions or recommendations for valve or orifice size in motor catalogs for flushing flow, so the selection of flushing valves is a challenge.

Of course, you can find orifices (with different diameters) provided by the manufacturer with the motor in the motor’s catalog. But the flow and result case temperature will be different from application to application and the selection of the correct orifice is an engineering responsibility without any help or advice from the motor manufacturer.

Moreover, the manufacturer can’t provide all range of orifice diameters so the selection in the catalog is usually limited. And as you can see, sometimes values of flushing flow can be really huge and the only experience helps me to select the right flushing valve size at the beginning of the project.

I still believe, manufacturers can provide some diagrams/charts with correlation “power -> flushing flow” for approximate/preliminary estimation of the flushing valve size. Because I do not think everyone has a chance to make long tests during production and play with valves sizes…

What do you think?

Rexroth A4VG clones

Just in case if you need replacement for Rexroth A4VG, it seems to me these guys are brothers:

Rexroth A4VG Parker C-series Dana Brevini S6CV
Rexroth A4VG Parker C-series Dana Brevini S6CV
Available Displacements:
28cc, 40cc, 56cc, 71cc, 90cc, 125cc 55cc, 81cc, 136cc 75cc, 128cc
Nominal pressure:
400 bar (5800 psi) 420 bar (6090 psi) 400 bar (5800 psi)
Maximum Permissible Fluid Cleanliness:
20/18/15 20/18/15 20/18/15
Operating temperature:
−25..+110 °C -25..90 °C -25..90 °C
Viscosity range at operating temperature:
16..36 cSt 15..40 cSt 15..40 cSt
Available control systems:
HD” Proportional control, hydraulic C” Hydraulic proportional control with internal feedback HIR” Hydraulic proportional with feed-back
EP” Proportional control, electric F” Electric proportional with internal feedback HER” Electric proportional with feed-back
ET” Electric control, direct operated, two pressure reducing valves G” Electric proportional without internal feedback HEN” Electric proportional without feed-back
EZ” Two-point control, electric E” Electric non proportional HE2” Electric on-off
DG” Hydraulic control, direct operated D” Hydraulic proportional control without internal feedback HIN” Hydraulic proportional without feed-back
– – – A” Manual lever HLR” Manual lever with feed-back

Semi-closed hydraulic circuits

Have you ever heard about the semi-closed hydraulic circuit?

The idea is to use open loop pumps in closed loop circuit. In the latest eighties, Mannesmann Rexroth (yes, that time Mannesmann yet!) even offered pumps A4VSH, especially designed for semi-closed circuits.

Bosch Rexroth A4VSH pump

Bosch Rexroth A4VSH pump, from catalog RE92110/01.89

The main difference between closed loop pumps and semi-closed loop pumps was in addition block mounted to the ports A and B with check valves which let to supply suction flow from the tank, while mainstream comes from the motor to pump’s suction port:

Since that time Rexroth still builds A4VSH, but there are a limited number of sizes and options available and its no longer a mainstream published option.

But to make a semi-closed loop you do not need some special pump, it’s really easy to turn most standard open loop pump into a semi-closed loop circuit. Of course, you have to have some knowledge about the application and actuators before trying to apply it. If the pump does not have an integrated boost pump and check valves these are commonly added via an external gear pump and external check valves.

Here is the simplest example of the semi-closed circuit schematic where a regular open loop pump with LS control is involved to run two motors with independent proportional control of their speeds: