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Radial Piston Pump

Radial Piston Pump

Radial Piston Pump

We are using as radial piston pump which is having seven pistons. The pump rotates at 1440 RPM and delivers 24 litres of oil per minute. The pump is a closed type pump and sucks oil from a high level tank. We have connected a 1 - 1/4" hose to the suction line of the pump. The through and through bore of the hose fittings is 1". The suction line of the pump comes from a 3" suction filter. (We have deliberately used an over sized filter to avoid clogging). As in any radial piston pump, it has a suction and delivery valve for each piston. The image of the suction valve is attached herewith.



The delivery valve is just a 3/8" ball seated on a disc, backed by a spring.

Now my problem:

The pump runs smoothly for about a month. After that - while running idle - the suction valves of the pump begin to create a noise (tak-tak-tak-tak). As soon as we pressurize the pump up to 70 bars, the noise goes away. Again when the pump returns to the idle position, the noise re appears.

We dismantled the pump, opened the suction valves and applied lapping paste on its seat. Lapped it and then again fit it. Now on running the pump there is no noise. But again after running for a month or so, the noise again re-appears. Again on pressuring the pump up to 70 bars, the noise goes away. We have repeated this process a number of times, but every time the noise comes again after some days of operation. We have checked the cleanliness of the oil too. Changed the oil (we use Hydrol 68 hydraulic oil). Cleaned our reservoirs. But still not helped.

We asked the manufacturer about the material of the valve. They say it is Mn 20 Cr 5 garde steel. We made the valves from En 28. But in vain. The noise re appears again.

Please help. What could be the reason.

RE: Radial Piston Pump


You mention that the noise occurs "while running idle", and that the noise goes away when you increase pressure to 70 bar.

I assume that the suction piping comes from a tank/reservoir at atmospheric pressure, and that the 70 bar measurement is the discharge pressure.

What do you mean by running idle? Do you mean that the pump is being run by a motor, but has little or no flow? Does this mean that it's providing normal flow at a much lower pressure? Please explain.

The pictures you posted show dark spots that look like carbon deposits. I also assume that those pictures show internal components from the suction check valves. Is that what these are?

I wonder if you're getting a low/no flow condition during this idling. That might allow the check valves to slam shut and create the carbon deposits through a diesel-like process. I haven't seen that with hydraulic systems myself, but I've had it happen with spring-piston systems using lubricating oil (pellet guns).

RE: Radial Piston Pump

Thanks for the reply. We use this pump on a hydraulic press. The pumps goes up to 230 bars maximum pressure. The pressure is intermittent and is retained over a check valve.

Yes .. the suction piping comes from a tank/reservoir at atmospheric pressure, and that the 70 bar measurement is the discharge pressure.

The pump is coupled with a 15 HP 1440 RPM electric motor. By running idle I mean to say that the pumps sucks fluid and discharges it into the P port of a direction control valve. The P port is normally connected to the Tank port. So when running idle - the pump simply circulates the oil back to the tank. There is no pressure in the discharge line while it is running idle.

After some days of operating the pump, it delivers 24 lpm of oil while running idle but the suction valves start making a noise.

Yes the picture shows the suction check valve. The valve shows carbon deposits because it was hardened. The valve seats on the face. Please check the image attached. If we lap this seat and fit it again, the noise goes away -- but re appears after some days.


I am getting full flow while idling - as stated earlier -- but the suction check valves start producing a sound. Also please see this video.


As soon as the press is actuated, the sound disappears. But when the pump idles - the sound re appears.

Awaiting valuable suggestions to come out of this problem. Thanks..

RE: Radial Piston Pump

This is an educated guess at this stage.

It sounds like one of the suction valves is having trouble closing when the pump is unloaded. When the pressure in the outlet port rises, there is enough pressure to cause the valve to be "forced" closed.

I would suggest that you look at the side of the stem on the suction valves, see if there is evidence of wear.

Of course, if there is one valve that cannot close, the pumps will be unbalanced and thus noisy.

No promises, just something to check.



RE: Radial Piston Pump

Do you have a photo of the inlet valve seat surface before you rework it?

RE: Radial Piston Pump

Thanks once again for the replies. I agree with your point Adrian. We were thinking of increasing the tension of the spring to keep the valve closed even while pump is idling. Regarding the stem of the valve, I am attaching some images of the valve and the pump.


I also think that the stem of the valve is not ground fit into the housing. So the guide is not proper. So I think the manufacturer has seated the valve on its face - to compensate the misalignment due to poor fit. (The stem is only 4 mm in diameter). I am modifying the valve to make the stem to 5 mm and grind it and fit it in the housing. The seating of the valve and the housing, I am making it 45 degrees. This I think would help in self centering the valve onto its seat - and I think that will keep the valve on its seat even at low pressures i.e while idling.

What is your opinion ??

RE: Radial Piston Pump

Oops I forgot to mention.. tbuelna ... The images of the valves are that of the inlet valve seat surface before we rework it.

Valuable suggestions awaited....

RE: Radial Piston Pump

The short bearing surface and the large clearance around the stem suggest that the valve is intentionally 'loose'. Tightening up the stem clearance might make the valve overconstrained. Using a stiffer spring might starve the pistons of oil, reducing capacity and perhaps leading to scoring.

I'm inclined to believe the valve was designed as it is, at least partly because of bad experience with prior generations, and that embarking on a development program for a new valve in a production environment could get very expensive.

Aside from the noise, is there any other ill effect of leaving the valves in operation beyond a month? Do pieces of the valves appear in the oil? Does the oil temperature change? Does the press work differently? Does the noise ever go away? Does it get worse?

I.e., at this point, if there's no suggestion of other trouble related to the noise, I'd fit an acoustic blanket over the valves and leave them alone until something bad happens.

Mike Halloran
Pembroke Pines, FL, USA

RE: Radial Piston Pump

The first idea that seems to me the most plausible:
With video it seems that the noise comes from oil suction with air. When the pump has been switched off the return fluid in the reservoir must induce an emulsion in the tank. We can try to put more oil in the tank to see if the sound changes. Then if you can watch an upper inspection hatch of the tank, see if there is not a big oil emulsion while the pump is disengaged. The problem may come from a return pipe of the fluid which is located above the level of the fluid, or an oil spill on top of an inner wall of the tank.
Second idea:
Check the pump stop that coupling is not abnormal angular play.
3rd idea:
Regarding the suction valve must not increase the force of the spring because we have only the air pressure to force-feed the pump.
Fourth idea:
The large bearing causing the eccentricity can have a ball cage that is damaged and causes noise when the bearing on strengths decrease.
5th idea:
Remove the filter cartridge to see if you do not have too much vacuum aspiration. The springs which must be plated pistons against the bearing may have trouble pushing the more so as the pump piston is worn the oval bores.

RE: Radial Piston Pump

The first picture linked in your third post shows some interesting damage to the outer edge of the seat surface at the 11-12 o'clock position. It looks like it could be cavitation damage.

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