Adjust Hydraulic Pressure Relief Valve

[Trent62]

Recently purchased a used JCB 1CX. I attached a snowblower to the high flow circuit of the machine and it does not perform as one would expect. The blower calls for 55 lpm. From the specs I can locate it appears that the displacement rating for the high flow circuit on the machine is 90 lpm @ 3600 rpm. It says the maximum working pressure is 2785 lbs. (although these specs are for a serial number before mine). To me it seems that the high flow circuit should have more than enough capacity to run that blower. However, I have to go painfully slow with the blower through the snow or it just won't throw it far enough, it will just kind of flop out of the chute. I had someone put a flow meter on the circuit and they got 94 lpm of flow at zero pressure. As he turned up the pressure resistance at the meter it dropped to 54 lpm at 2000 lbs. pressure resistance at which point the sound changes as if the pressure relief valve opens. I get the same sound if I load up the snow blower with snow... one can hear what I would describe as very pronounced "hissing" noise which I am guessing is coming from the pressure relief valve opening prematurely. I have a few questions.

First, is it typical for the flow rate to decrease as the pressure increases or should that circuit provide 90 lpm at 2785 lbs. pressure?
Second, is this particular relief valve adjustable and where can I find it?
Is there anything else I should look?

Thanks.

 

[Huntoon]

You're probably limited by horsepower.
HP = (PSI X GPM) / 1714

90*2785/1714 = 146 horsepower.

Your machine doesn't have that capacity, so it throttles back the flow when you need more force.

 

[Trent62]

You're probably limited by horsepower.
HP = (PSI X GPM) / 1714

90*2785/1714 = 146 horsepower.

Your machine doesn't have that capacity, so it throttles back the flow when you need more force.

Thanks Huntoon. I gave you the flow in "litres" per minute. 90 litres per minute is actually just under 24 U.S. gallons per minute.

24*2785/1714 = 39 horsepower (If I understand correctly). The machine is over 50 h.p.

 

[Delmer]

But he's in Canada and Liters per minute would work out to about 40HP

Are your hoses and couplers big enough to handle that flow? The pressure the pump/relief valve/"regulator" sees is what matters, did you measure the pressure close to the pump? I'll stop speculating now...

 

[Trent62]

The hoses and couplers are factory so I am guessing they are big enough. The flow was measured by disconnecting the hoses from the hydraulic motor on the blower and putting the feed in one end of the flow meter and the return hose on the other end of the flow meter. When the meter was wide open, allowing full flow with no resistance we were getting 94 litres (24 gallons per minute). As the flow was restricted, by turning the valve on the flow meter to offer resistance, the flow dropped down to 54 litres per minute (14 gallons per minute) at 2000 psi where it seemed to force the relief valve open. I'm guessing that the relief valve should not open at 2000 psi and I am told there should be an adjustment on it. I think that if the relief valve did not open until 2785 psi (or more) then my blower would not bog down as easily as it does. Doesn't that make sense?

 

[Tones]

Yep screw the pressure relief up. Because the pressure down then you should also consider the cause, is the pump worn or any internal leakage. The pressure test should also be done at the pump as it would help find the problem. When testing at the implement end of the circuit you should allow for losses in transmission which can be up 20%.

 

[Trent62]

Tones,
If a pressure relief valve is not supposed to open until 3000 psi and it opens at 2000 psi wouldn't the only cause be either too low a setting or a faulty relief valve. I would think that regardless of leakage or a worn pump that the valve should not open until the system builds pressure in excess of the valve setting. Am I not understanding something?

 

[Tones]

Trent,
you're not misunderstanding anything. First sentence of my post " Yep, screw up the pressure relief". All I am eluding to is that on older equipment things need to be checked a more thoroughly. I own an older tractor and if I was to pressure and flow check it, it would be done at both ends of the circuit, no if's or buts. Without checking the how do you know it's the pressure relief? Could be the pump is maxing out at 2000psi.

 

[Trent62]

I understand. Thanks Tones.

 

[Delmer]

I don't know a JCB skidsteer from a JD skidsteer, so take it for what it's worth.

A simple gear pump system has a relief valve, but a piston pump (or combining two pump flows?) will have more complicated controls. There might be more to fixing the problem than just turning up/down the relief valve.

 

[Cmark]

To partly answer your first question, yes, it's normal for the flow to decrease as the resistance (closing the valve on the flowmeter) increases.

If you were seeing 94 l/m at zero pressure, you would not expect to see the same flow at 2000psi.

 

[Trent62]

Delmer,
I guess the best course of action would be to find the high flow valve and locate the relief valve on that circuit. The easiest thing to do would be to turn up the relief valve and see if that fixes the problem... if not, then I need to look further.

Cmark,
So, flow will drop as pressure increases... makes sense. The manufacturer of the snow blower says it requires 55 - 62 l/m. Would you expect that would be at a certain pressure then or at zero pressure?

 

[Cmark]

Delmer,
I guess the best course of action would be to find the high flow valve and locate the relief valve on that circuit. The easiest thing to do would be to turn up the relief valve and see if that fixes the problem... if not, then I need to look further.

Cmark,
So, flow will drop as pressure increases... makes sense. The manufacturer of the snow blower says it requires 55 - 62 l/m. Would you expect that would be at a certain pressure then or at zero pressure?

Yes, your manufacturer is only giving you half the information. They should quote XXX flow at XXX pressure.

You can find the relief valve which is affecting the aux circuit and adjust it to maximum spec, but I suspect it won't make much difference. You already know the blower won't throw the snow as it should before the relief valve opens, which means the flow below 2000psi is inadequate for the attachment.

Unless the machine has some sort of computer controlled programmable flow limiter, I think you're going to arrive at the conclusion that it just isn't up to the job.

 

[lantraxco]

Without a manual or schematic it's impossible to be sure, but I would guess you have two separate pumps on this machine, one for standard implement flow, the other to provide the other half of the high flow oil. You will always see some drop in flow as pressure increases, but more than about 10% indicates either a very worn pump, or a bypass situation somewhere in the valving. I have seen relief valves with worn seats do this sort of thing for instance. Can you switch to standard flow and have you tried checking flow and pressure that way? Should be 45-50 liters per minute at 3,000 psi roughly according to the brochures I could find. Really need a schematic to identify the flow path and what items to check for malfunction.

 

[Trent62]

The machine blows snow just fine until I load it up and I hear that very pronounced "hissing" noise which I am "guessing" is the relief valve opening. I've drawn (or jumped) to this conclusion because when I had the flow tested I got the same "hissing" noise when the pressure maxed out at around 2000 psi when it should have continued to build pressure to around 3000 psi. The machine only has around 800 hours on it so I figured a pump problem would be unlikely, maybe I'm wrong, or maybe the machine has way more than the 800 hours showing. Is it likely that the pump would be the problem on a machine with 800 hours? Looks like I am going to need a mechanic with some test equipment.

 

[Tones]

Yeh Trent, s**t can happen with hydraulics at any time. I have a new forestry mulcher that lost all power to the mulcher head at 40hrs total time. From that experience is what I have posted- check every thing-not what you may think., that includes the snow blower.It also may have valves that may need setting or even a crook hyd motor all of which can cause a hissing noise which can be transmitted through the lines.

 

[Trent62]

Just an update. I located the pressure relief valve and turned it up gradually for a total of about 1-1/2 turns. The thing is now like a new machine... throwing heavy wet snow 30 feet or more. I have no idea what pressure it is set at so I will likely get that checked out soon. Thanks for all the advice guys!

 

[kshansen]

Just an update. I located the pressure relief valve and turned it up gradually for a total of about 1-1/2 turns. The thing is now like a new machine... throwing heavy wet snow 30 feet or more. I have no idea what pressure it is set at so I will likely get that checked out soon. Thanks for all the advice guys!

Good to know it's throwing snow for you now but don't fail to get the pressure tested! You do not want to be out blowing snow in subzero temps and have a hose or pump rupture from too much pressure