Radial piston pump heats up at recommended pressure 2

[AamerK]

Hello,

I'm a technician at a concrete products plant, and we're having problems with our hydraulics.
Our main pump is a radial piston pump (Moog D954-2011 RKP 63) & the problem is that if we set the pressure to the recommended 200bars then the pumps' body heats up very quickly(10-15mins), the oil in the tank doesnt heat up that much, currently we have set it to a measely 120-130 bars to keep our machine running although at a very slow speed ofcourse.

The setup is shown in the drawing attached.
Things we have already tried:

1) Replacing the pump with a spare
2) Checked the pressure relief valve(unadjustable, fixed at 280bars)

Is it possible that both the main pumps are worn out?
Also, if we set the pressure to 200bars, then the 30KW motor running the main pump also starts drawing too much current.

 

[AamerK]

https://files.engineering.com/getfile.aspx?folder=57f9a70e-be14-496e-932d-d3a2addb7321&file=Pump.jpg

 

[LittleInch]

This document looks quite useful

http://www.moog.com/content/dam/moog/literature/ICD/Moog-Pumps-RKP-Catalog-en.pdf

Depending on your motor speed ( 1500 or 1800 rpm?) on page 7 and especially page 9 you can see that at 200 bar, the power required is over 30kW, so not surprised your motor is drawing excess amps.

Do you have access to the pump data sheet or any plate stamped on the pump itself.

you say the pump heats up, which is unsurprising as you're putting 30kW into the thing with not a lot of flow to take that heat away.

Also see

http://www.moog.com/content/dam/moog/literature/ICD/Moog-Pumps-RKP-Catalog-en.pdf

and look a the manual page 24 on says the same thing for your power rating.

Hydraulic fluid temp range is quoted up to 80C




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[LittleInch]

Actually are you operating the pump at its max fluid rate of 80l/min or is it recycling within the pump unit? What is the forward hydraulic fluid flow?

Also there seems to be various ways to control the operation of this pump. Which mode of operation are you using?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[3DDave]

The catalog seems to suggest an efficiency of 90-95%, so of the 30kW, about 1.5 to 3kW is lost to heat in the pump. There is a recommendation that a flushing line be used to supply 4-6 lpm, especially at low pressure and low flow. I don't see that connection on the diagram.

 

[hydtools]

Maybe the case drain is blocked or disconnected.

Ted

 

[Jacc]

Wouldn’t a blocked drain port cause the shaft seal to blow?

 

[TimSchrader2]

Hello

Do you have the press compensator option to destroke the pump to lower GPM to reduce amp draw and heat input? Or is it adjusted correctly.

It should be adjusted to start working about 300psi below the relief. If the relief is doing the relieving instead of the compensator the pump will not destroke. If so the relief will be real hot also.

I am more familiar with the axial piston pump, but I believe the press compensator functions the same with a radial piston.

 

[AamerK]

LittleInch

Thank you for the response.

We have a 30KW, 1500rpm motor attached with this pump- thats just how it has been designed by the machine manufacturer. But i get that its not a biggie if its drawing full amps since thats just how much power is required by the pump.

The exact model number of the pump is HPR18A1RKP063KM28J1Z00
I know that this pump has a combined pressure & flow compensator(which is adjusted to full setting on the pump) & my understanding is that, with this type of pump, when no flow is required, the sliding ring centers itsself and the pistons no longer supply more oil until there's a pressure drop (due to a cylinder working).

As far as the output flow is concerned, its a fully automatic machine with a number of cylinders working all the time(except for a few seconds now and then), I've attached the full hydraulic drawings of the system(in autocad format) if anybody is interested. But then again with a flow compensator i think it shouldnt be a big problem even if its idle for a few minutes or should it?

 

[AamerK]

3DDave

Thanks for your response.

We have 2 water-cooled heat exchangers & one air heat exchanger installed on this system(those who are looking a the drawings will only see 1 heat excahnger but we made this addition 3-4years ago) we know that the combined capacity of these heat exchangers is greater than 7-8KW, which is sufficient even for summers, and right now the weather is quite cool.

Also, the oil itself remains cools, the pumps body just gets very hot & the pressure starts to drop drastically.

 

[AamerK]

hydtools & Jacc

The case drain line is present and clear of any blockage, we havent measured the flow through the case drain line of these pumps yet, but we know that it's not choked.
Can anybody guide me on what should the case drain flow would be like when the pump is at full stroke & no cylinder is being actuated? From what ive read its supposed to be between 1-5% of pump flow rate?

 

[AamerK]

TimSchrader2

The pump does have a pressure and flow compensator, it was preadjusted to maximum setting by the OEM, now i'm not sure if this setting was ever changed, but i do know that the line going from the pressure relief valve(fixed 280bars) to the tank is always at ambient temperature(so i reckon that theres no oil flowing through that for the most part).

There is also a second relief valve on the pump(shown on the left side of the valve-Y444 in the drawings) only this valve is used to control the pressure output of the pump(since its recommended that the pumps pressure & flow compensator should remain at its pre-set position), do you think maybe theres a mismatch in the setting between this secondary relief valve and the pumps compensator? I don't really understand the need for this secondary relief valve really.

I'm attaching an actual picture of the pump and ive marked the relief valves etc if that helps.

 

[TimSchrader2]

Hello


Pretty Much to Quote #1. Except the pump will destroke at any time the cylinders require more then the max pressure compensating setting. Which should not happen in your fixed set up. If someone trys to overload a cylinder just a bit, the pump will destroke first, and if they really overload it the relief will kick in.

We have whats called a load sense on our pump, which may be the same as the 'Unloader'. I am not sure. Anyways, When the pump is on and no functions/cylinders are working the Pump ramps down to about 200psi and the motor just hums at a very low amperage and just bleed flow. A press compenstor may destroke but does not lower the pressure so Motor is still working somewhat hard. But, Not full amps. The unloader could relate to a torqe unloader. I only used this a few times on a crane to reduce the amp draw when operating the crane at full speed and when not lifting a load, which requires less pressure. These are tricky to set with the press comp settings.

OP Quote #1
I know that this pump has a combined pressure & flow compensator(which is adjusted to full setting on the pump) & my understanding is that, with this type of pump, when no flow is required, the sliding ring centers itsself and the pistons no longer supply more oil until there's a pressure drop (due to a cylinder working).

OP QUOTE 2
i think it shouldnt be a big problem even if its idle for a few minutes or should it?

 

[AamerK]

TimSchrader2

So essentially i should check motors amperage when no function is happening, and compare it to when a cylinder is being actuated, if theres no difference then the pump is not destroking i guess.

 

[itsmoked]

I'd expect a 30kW hydraulic system to need a cooling system somewhere. Something more than a metal tank too.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[TimSchrader2]

Hello

The amperage will or should help define if the pump is destroking. But not as definitive as a flowmeter. You may need to check the no load amps and curve of the motor to get some idea of how close or how far from the FLA of the motor you should be when at low pressures. The motor will still take a good 5 of amps at no load. The vendor should be able to verify your data.
It is still possible that something is rubbing in the motor.

 

[AamerK]

Hello everyone, Im sorry for taking this back up after a long time.

We figured that the pump is perfectly fine & is able to destroke after reaching set pressure(at this point the motor is virtually at no-load). Case drain flow is less than 1 l/min.
However there is a main valve(Y445 in the drawing) that allows the pressure from the pump to go to all the manifolds. As soon as this valve opens, the pressure drops to 150bar immediately & at that point the pump is unable to destroke because its always trying to reach 200bars. Also we see that there is a sudden rush in oil flow to the tank from the main tank line.

Now, how can i figure out what is allowing the oil to drain into the tank, because we can hear the oil, but we can't see where exactly is it coming from. Maybe a valve is bypassing all the oil to the tank?

 

[Stick.]

Does your pump have a stroke indicator on it? If it's running at 150 bar and pumping a meaningful amount of fluid, there will be heat generated somewhere along the way when the pressure drops from 150 to 0 bar. If you have access to an infrared thermometer or preferably an IR camera, you can use that to check each valve/component (after the system has been running and bypassing long enough to build up some heat) to find out where the heat is being generated and then focus on that area. If you don't have either IR tool, you can use your hands to check things as long as you're very careful not to burn yourself. Either start at the pump and work your way towards the tank (checking everything along the way), or start at the tank and work in the other direction.

 

[hydtools]

It sounds like the manifold is allowing fluid flow to tank through y444. Or some function downstream of the manifold is returning flow to tank through y444.

Ted

 

[AamerK]

Stick.

Thats really helpful, I dont have in IR camera, but I'll try looking for hot-spots by hand or a simple contact temperature sensor. If that doesn't work i'll get an IR camera.

Also, the pump doesn't have a stroke indicator, we just use a simple clamp meter on the motor to see how much amps its drawing, there is a clear difference between stroke amperage(25-30A) & destroked(9-10A).

I'm sure there is a meaningful amount of fluid flowing- I get this from the sound of fluid flowing through pipes & also the rubber hose on the tank line gives a strong jerk everytime this valve actuates.

I'll post about whatever comes up.