Adjustable gear pump?

[stevieb49829]

Is there a way to adjust the output pressure on a typical hydraulic gear pump, or will I need to add a regulator and a bypass circuit? The engine-mounted pump on my Massey Harris is too much for the orbital valve on my "farmerized" power steering. Its putting out 2-3000 psi, and I'd like it down around 1000. steve

 

[Jim.ME]

A relief valve set to 1000 psi with a return to reservoir would do it

 

[used red MN]

A relief valve set to 1000 psi with a return to reservoir would do it

First off a gear pump is considered a “positive displacement” pump, beyond a circuit allowing discharge bleed off the output can only be varied by changing the rpm. Starving the suction of the pump is a no no because of the many problems that come from that. I would suggest looking into a flow divider such as I have linked. I think it may allow for less fluid heating compared to a relief valve.
Flow divider
Edit: Looking more I think it might also warrant getting a flow control valve with a relief incorporated into it as well such as this. Flow & relief valve
They also have that unit with 3/4 NPT ports as well if preferred, it is within $10 difference for that one.

 

[DanielW]

I wouldn't want to do that with a relief - especially in a power steering and open-centre system. It'll only be a minimal amount of time (when turning) that it's not dumping. I suspect the heat you'd create would be something fierce - you'd be boiling your hydraulic fluid in short order. If you're getting 3000 psi from that pump, I suspect it's not OEM and is a pump, but is rather that's been added on?

I don't think a flow control is the right answer either. You'd essentially be relying on the pressure drop through the restriction of the divider, but that's going to achieve steady-state at full psi when you're not turning, and the pressure drop you'd achieve when turning would be very much dependent on how fast you turn. A flow control is meant to divide and control flow, not pressure.

A proper pressure reducing valve would, I think, be the answer (the regulator and bypass-to-tank circuit you mention). And it would be the same amount of plumbing as a divider or relief. They function similar to a relief, but are normally-open (unlike reliefs) and are meant for continuous flow applications - they wont create oodles of heat like a relief will. I'm not sure what's available for an off-the-shelf reducing valve, but I'm sure there are some. The cheapest/easiest option might be to just get a basic reducing cartridge from somewhere like Sun that's rated for your approximated steering GPM and a basic in-line Sun single-cavity manifold and plumb it accordingly.

But before you go that far: I'm curious what you're using for your orbital valve and cylinder, and what problems it's causing? I'm also curious what's causing the wide variance in pressure? You mention 2-3000 psi: That's a big range, and a lot of pressure for any hydraulic demands of any MH. In an open centre system like that, the pressure you see should really only be a function of the pressure required of the application. Ex., if you properly plumb an orbital valve in that open-centre system, you should only measure pressure when there's a demand on the system (when turning the wheel, or using the remotes), and the pressure you measure should only be that required to steer the tractor pr operate the remote cylinder (that's not an entirely-true statement, but true enough for our purposes). The 2000-3000 psi you're seeing sounds suspiciously like something is up with the plumbing and it's dumping over the pump's internal relief (which is probably set in the 2500-3000 psi range).

Where in the system are you measuring that pressure? I'm making a few assumptions about the system, so apologies if I'm assuming anything incorrect or that you've already thought of. With an open-centre system like that, you should have (fairly) negligible pressure when no load is applied (if it's just sitting there idling or cruising along with no demand for hydraulic power). If you're seeing that kind of pressure constantly, it sounds like something else is up - possibly an aftermarket pump not plumbed to tank correctly, or the pump output plumbed directly to the orbital valve with no return to tank (or the wrong type of orbital valve). Perhaps most critically: Is your orbital valve for an open-centre system (they make them for both open and closed systems). And, if the orbital valve is for an open system (hopefully it is), is the tank return line from the valve plumbed correctly?

If you're seeing that kind of pressure only when steering, however, that gives rise to the question of why it takes that much pressure to steer? Too small cylinder? (doubtful - it shouldn't take much, depending on how your cylinder is mounted and the pivot geometry). Or is it that it's working but you're seeing a vague or slow steering response? In which case maybe a smaller cylinder is the answer.

 

[Jim.ME]

I should have asked before, is this pump supplying just the steering or did you just tap the steering into an existing pump supplying other circuits the steering? How many GPM is the pump? A sketch of the current circuit would be good.

 

[stevieb49829]

I'll get back in a day or two to answer your questions. But the short of it is its a dedicated aftermarket gear pump rated at 2500 psi, but off hand I don't remember the flow rate. It runs off the cam gear, being directly behind the governor on the Continental F162 engine. It supplies an orbital valve off a MF 245 power steering system and a 2" x 10" dual action cylinder pushing the tie rods. The orbital valve has an appropriate return to tank and is an open center system. Every so often the pressure will escape the new seals on the orbital valve shaft, so I'm assuming the pump is overpowering the orbital valve design. I'll modify my flow if I can, or I'll switch to a belt driven power steering pump that produces less pressure. The steering itself works as intended. steve

 

[Jim.ME]

Likely not the answer you want but a belt driven power steering pump would seem like a better answer than the gear driven pump. They are designed for dedicated steering supply, make less pressure, and many have a relief valve built in. JMHO

 

[stevieb49829]

Likely not the answer you want but a belt driven power steering pump would seem like a better answer than the gear driven pump. They are designed for dedicated steering supply, make less pressure, and many have a relief valve built in. JMHO

I'm considering that Jim. I'll have to design a pump mount for the engine once I choose a pump, but I'm not averse to making the changes. I don't like dribbling hydraulic fluid every once in a while. Then I could put the pump on my other tractor, build another 3 point for that one, and probably sell it faster with a 3 point. steve

 

[Jim.ME]

I'm considering that Jim. I'll have to design a pump mount for the engine once I choose a pump, but I'm not averse to making the changes. I don't like dribbling hydraulic fluid every once in a while. steve

I haven't researched to see if the same mounting and drive set up would work but some later MF tractors with Continentals had engine mounted, gear driven pumps with reservoirs.

 

[Brendon-KS]

Technically speaking a gear pump (or any pump, for that matter) does not produce pressure, it only produces flow. What pressure is developed in the circuit is entirely dependent on what is downstream of the pump. The pressure rating of a pump only tells you what the pump is physically capable of without worrying about wearing it out prematurely or, worst case, breaking it. A positive displacement pump (which a gear pump is) will put out X gpm flow at Y rpm and this flow MUST go somewhere or something WILL break. If your circuit can't handle the flow that is provided by the pump and you limit the pressure with a relief valve you will get lots of heating and poor efficiency since you'll have flow going over relief all the time. From what you describe you have a circuit that is being supplied more oil than it can handle without the pressure getting too high.

 

[DanielW]

Technically speaking a gear pump (or any pump, for that matter) does not produce pressure, it only produces flow. What pressure is developed in the circuit is entirely dependent on what is downstream of the pump. The pressure rating of a pump only tells you what the pump is physically capable of without worrying about wearing it out prematurely or, worst case, breaking it. A positive displacement pump (which a gear pump is) will put out X gpm flow at Y rpm and this flow MUST go somewhere or something WILL break. If your circuit can't handle the flow that is provided by the pump and you limit the pressure with a relief valve you will get lots of heating and poor efficiency since you'll have flow going over relief all the time. From what you describe you have a circuit that is being supplied more oil than it can handle without the pressure getting too high.

Exactly what this guy said; he stated it more simply and eloquently than I did above. Possibly it's only over-pressuring when you get to the end of your cylinder stoke and dead ends? In which case it should dump through the relief. In which case it may just be a case of turning down the pump's relief. I assume the aftermarket pump has an in-built relief? If not, you need to add one.

 

[wore out]

I'll get back in a day or two to answer your questions. But the short of it is its a dedicated aftermarket gear pump rated at 2500 psi, but off hand I don't remember the flow rate. It runs off the cam gear, being directly behind the governor on the Continental F162 engine. It supplies an orbital valve off a MF 245 power steering system and a 2" x 10" dual action cylinder pushing the tie rods. The orbital valve has an appropriate return to tank and is an open center system. Every so often the pressure will escape the new seals on the orbital valve shaft, so I'm assuming the pump is overpowering the orbital valve design. I'll modify my flow if I can, or I'll switch to a belt driven power steering pump that produces less pressure. The steering itself works as intended. steve

If you don't have a relief in place and are "deadheading" a gear pump with no relief in the system to tge steering valve you are darned lucky the pressure hose hasn't blown, or the pump hasn't split open or the timing gear train hasn't been broken!

 

[wore out]

I'll get back in a day or two to answer your questions. But the short of it is its a dedicated aftermarket gear pump rated at 2500 psi, but off hand I don't remember the flow rate. It runs off the cam gear, being directly behind the governor on the Continental F162 engine. It supplies an orbital valve off a MF 245 power steering system and a 2" x 10" dual action cylinder pushing the tie rods. The orbital valve has an appropriate return to tank and is an open center system. Every so often the pressure will escape the new seals on the orbital valve shaft, so I'm assuming the pump is overpowering the orbital valve design. I'll modify my flow if I can, or I'll switch to a belt driven power steering pump that produces less pressure. The steering itself works as intended. steve

If you don't have a relief in place and are "deadheading" a gear pump with no relief in the system to tge steering valve you are darned lucky the pressure hose hasn't blown, or the pump hasn't split open or the timing gear train hasn't been broken!

Likely not the answer you want but a belt driven power steering pump would seem like a better answer than the gear driven pump. They are designed for dedicated steering supply, make less pressure, and many have a relief valve built in. JMHO

Many have an internal flow control valve, as well, to help with P.S. down to idle without making excessive flow @ high R.P.M.'s

 

[Fritz Maurer]

A priority valve off an old combine. That slices off a constant 2 or 3 gpm for steering and the rest goes wherever it is needed.

 

[moresmoke]

Shaft seals not holding is typically a symptom of excess pressure on the return side. Same situation if you are running a motor or steering valve as you are. The cavity behind the seal is open to the return port, and there should never be much pressure there.

As others have pointed out, something is not adding up with either your system or description. You absolutely need a relief valve between the pump and valve, could be part of the pump we don’t know. You can set the relief at whatever pressure you want.

 

[stevieb49829]

If you don't have a relief in place and are "deadheading" a gear pump with no relief in the system to tge steering valve you are darned lucky the pressure hose hasn't blown, or the pump hasn't split open or the timing gear train hasn't been broken!


Many have an internal flow control valve, as well, to help with P.S. down to idle without making excessive flow @ high R.P.M.'s

I may be assuming that the open center orbital valve is supposed to allow excess flow to return to tank. Does it have an adjustable flow bypass designed in? And it does not appear that my pump has any kind of adjustable flow control. It is just relying on a proper open center system to handle it. steve

 

[stevieb49829]

Exactly what this guy said; he stated it more simply and eloquently than I did above. Possibly it's only over-pressuring when you get to the end of your cylinder stoke and dead ends? In which case it should dump through the relief. In which case it may just be a case of turning down the pump's relief. I assume the aftermarket pump has an in-built relief? If not, you need to add one.

I think that's what I was saying, Daniel. There is no external adjustment on my pump. Is there potentially an internal adjustment that can be made to reduce the pressure it is capable of providing, or how do I provide that adjustment outside of the pump. steve

 

[used red MN]

I may be assuming that the open center orbital valve is supposed to allow excess flow to return to tank. Does it have an adjustable flow bypass designed in? And it does not appear that my pump has any kind of adjustable flow control. It is just relying on a proper open center system to handle it. steve

Yes they are designed to send flow not needed for steering back to the reservoir. However most are designed to work off of a lower GPM feed, a rough number of 5 GPM or less.
As far as your pump, many are designed with a build in protection relief so deadheading doesn’t break parts of the pump. Usually if you see a hex cap somewhere on the pump that houses the relief. However, some do not have this and as has been said by others dead heading such a pump leads to something being damaged.

 

[DanielW]

I think that's what I was saying, Daniel. There is no external adjustment on my pump. Is there potentially an internal adjustment that can be made to reduce the pressure it is capable of providing, or how do I provide that adjustment outside of the pump. steve

Ah, I think we're now getting a better picture of your setup. I think we're now just differing in our lingo. You're not really looking to 'adjust the pressure the pump is producing' (probably capable of oodles of pressure if you just consider the pump and no relief). Rather, I think you're looking to adjust the relief pressure at which the pump blows by the relief if something deadheads: Which will happen periodically in a steering system when you turn the wheel to full stroke and it dead-ends. In that case, you want to limit the pressure with a relief.

Or to say it differently: The way you first mentioned it, it sounded like you wanted to limit the pressure the pump was producing all the time. And our replies (simplified) were more-or-less saying "Well, you shouldn't really be producing any pressure most of the time". But if it's rather that it's just causing issue when deadheading (when fully stroked), then that's just a case of needing to blow by the relief in these occasionally deadheaded instances, which is a typical setup.

Do you have a link to the pump you bought? Some pumps have a built-in relief. Some are adjustable, some are not. And some pumps don't have any relief at all and expect the installer to have their own relief. If your pump has a relief but is not adjustable, I suspect it's factory set to something very high (like 3000-3500 psi), and it's expected your system has a second relief that's adjusted properly for the equipment you're running. If your pump doesn't have any relief built in, you need to add one down-stream of the pump. Otherwise you'll blow out seals and possibly do more damage, because with no relief and a deadheading instance, the pump will just keep building pressure until something blows or breaks.

Once again I'm guessing here, but if you say it only leaks occasionally, I'd bet dollars to buttons it's only leaking when you fully stroke the wheel and deadhead it for a second every now and again. In which case it just needs a lower relief setting. It doesn't sound like your pump has an adjustable relief (and might not have any relief at all). If it's one of the more basic, off-the-shelf gear pumps, it probably doesn't have any relief. So it's probably just a case of getting an off-the-shelf relief, plumbing it to your pump output, and dialing down the pressure. The relief will have three ports: one inlet, one outlet to your steering valve, and one outlet dumping to tank.

Something like this would probably be the ticket. Should be lots of places where you can buy one for less than $100: https://www.princessauto.com/en/adj...ImFmNBEM6magFIsBL3dA_ZNynadJ0SCRoCbLkQAvD_BwE

 

[Fritz Maurer]

Regarding your opening post, the pressure is not your problem, but too much gpm. You can still 3000 psi at the cylinders as long as you get the flow under control.

A simple little valve from the junk yard and a little plumbing and you can be there.

I had a 25 gpm pump on an F350 to run a salt spreader. But to mount the pump on the 460 took too much room and the P/S pump had to be eliminated.

To power the steering with the 25 gpm pump, I put a steering priority valve from a 151 combine in the pressure line off the pump.... the steering got the perfect amount of flow and the spreader got all the rest.

Is possible the spring in the valve could be adjusted to change the gpm split, but for my case it was satisfactory right out of the box.