Is this some kind of pressure relief valve?

[Fallon]

I'd look at it differently... You are having heat issues due to an improperly designed system (valves or hoses to small) or bad parts (valve leaking or partially plugged).

It could be the impliment is just mismatched to your machine. Overheating in the summer is one thing, but if you are having overheating problems moving snow something isnt right. Fix the stuff that isnt right rather than put a sheer bolt in as a bandaid. A sheer bolt isnt super likely to save your hoses & motor from the massive pressure spike when you close the valves powering that pump.

 

[Hilbilly]

It could be a setup problem but I've done testing to try and find the issue. Based on that I think a big part of the issue is the SS itself. This is what I've discovered so far.

1) At idle, the system pressure appears to be around 50 psi.
2) At operating RPM with no QC's, a 3' section of 1/2" ID hose connected between the 2 aux. ports the pressure is about 300 psi (no load here .. just flow from one aux back to the tank)
3) With 18' of 1/2" ID hose, QC's, cross over valve and blower running at operating speed (not blowing anything) the pressure on the inlet side is 950 psi and the return is 350 psi.
4) Removing the cross over, the inlet side (at operating speed) was 750 psi and the return line was 350 psi.

Based on these tests, I concluded the following;
1) the motor requires 400 psi to run the blower, with no load.
2) the cross over relief valve produces a 200 psi pressure drop,
3) the hoses and QC's produce a 50 psi drop.
4) the SS produces a 300 psi drop.

I took the SS into the Bobcat dealer and had them run a pressure, flow, temp test on the auxiliaries. With nothing connected, other than their measuring devise, this what they found: At 1000 psi back pressure (induced by them) the oil temp was 175 F, at relief pressure of 3000 psi the oil temp was 185 F and the flow through the auxiliaries was 14 gpm. The flow is great considering this a 20 yr old machine. They did not check the back pressure of the system with no external influences. I told them it was 350 psi and asked if that was normal. They gave me a confused look and then reluctantly said "that should be ok". I got the distinct feeling they didn't know. I also asked about the oil temps and they said that was normal. However based on information I found on a hydraulic oil website, the max operating temp for ISO AW46 hydraulic oil (that's what I'm using) is 164 F.

 

[aczlan]

I'd look at it differently... You are having heat issues due to an improperly designed system (valves or hoses to small) or bad parts (valve leaking or partially plugged).
It could be the impliment is just mismatched to your machine. Overheating in the summer is one thing, but if you are having overheating problems moving snow something isnt right. Fix the stuff that isnt right rather than put a sheer bolt in as a bandaid. A sheer bolt isnt super likely to save your hoses & motor from the massive pressure spike when you close the valves powering that pump.

This, IMO, your hoses are too small.
Per: Hydraulic Hose Size Selection Chart - Hydraulic Pipe Sizing

For 14GPM with 1/2" ID hoses, that is a flow of ~25 feet per second of flow (recommended FPS for pressure lines is 10-20FPS, 5-10FPS for return lines). That will be worse with the fittings to connect the crossover relief.
I might see about replacing the crossover relief with a 3/4" one.
The backpressure sounds a little high, IIRC, our L3830 has about 150PSI of back pressure at full throttle in the summer (closer to 300 or 500PSI in the winter IIRC) until it warms up.

Aaron Z

 

[Hilbilly]

I agree the hoses are too small. I was planning on replacing them with 3/4" hoses until I ran the above tests and discovered the 1/2" hoses and QC's are only responsible for 50 psi in the overall system. My understanding is that pressure buildup is causes heat. If this is correct, then biggest heat sources are; 1) the pump and blower at 400 psi, 2) the skidsteer at 300 psi, 3) the cross over relief valve at 200 psi and 4) the QC's and hoses at 50 psi. So improving the hoses would likely not make much, if any, difference. The most that could possibly reduce the overall system losses is 50 psi and I doubt it would be close to that. Since the motor and blower can't be eliminated the next items to improve or eliminate are 1) the skidsteer back pressure of 300 psi or 2) the cross over relief valve which produces 200 psi pressure. That is why I was thinking of removing it from the system and using a shear bolt. If I could find a less restrictive relief valve I might try that

I would really like to find the cause of the 300 psi back pressure in the SS and fix that too.

I may still replace the hydraulic hoses and fittings with 3/4" but at a cost of about $400 I'm reluctant to do that since the smaller hoses and fittings are not responsible for much of the system pressures.

I'm wondering if I am using the wrong hydraulic fluids and that is causing an issue. I am using AW46 but the owners manual states it should be Bobcat hydraulic fluid or SAE 10/30W motor oil. I have the Bobcat fluids and could change over to that. But not sure how to go about getting all the old fluid out. The specs state there is 23l in the tank and 32l in the system. So if I drain the tank and replace it with the Bobcat fluid there would still be 9l of AW46 in the system that would mix with the Bobcat fluids. I'm not sure if that would cause more issues, since I'm told different manufactures fluids should not be mixed.

 

[aczlan]

Sorry if I was unclear, I would replace just the 1/2" crossover relief valve with a 3/4" one (like: 3/4 NPT 3 GPM 15-3 PSI Hydraulic Cushion Valve | Prince Mfg | Brands | www.surpluscenter.com ) and use adapters to connect it to the existing lines (or, replace the lines from there to the motor and leave the 1/2" lines going over to the crossover).
Two other questions though:
1. Why do you have 18' of hose on a skid steer mounted snowblower?
2. Can you post a picture of the motor/crossover plumbing?

Aaron Z

 

[Hilbilly]

Aaron,

The reason the lines are so long is that I just guessed at the lengths I would need to try out the SS conversion on a temporary basis and I didn't want to be too short. As you can see from the pic the lines are definitely not short. The lines from the SS to the cross over are 6' long and the ones from the cross over to the motor are 3' long. At some point I will get shorter lines. Here is a couple of pics of the setup. I have other pics and if you want to see something specific, let me know.





If I could find that Prince valve around here I would get it. Being in Canada limits my options. I've looked on line but haven't found a source yet.

 

[aczlan]

Did you have the lines made up, or buy them premade? If you had them made up, I might take them back and have them change the ends to the sae 8 oring ends that your valve needs.
If you take the hoses off of the valve, do you see any restrictions in the valve itself?

Aaron Z

 

[Hilbilly]

Did you have the lines made up, or buy them premade? If you had them made up, I might take them back and have them change the ends to the sae 8 oring ends that your valve needs.
If you take the hoses off of the valve, do you see any restrictions in the valve itself?

Aaron Z

They were premade but the place I got them from will alter them if they were purchased there. That is a GREAT idea and thanks for that. The valve is very restricted as you can see from the pic. I want to find a less restrictive one.

 

[aczlan]

They were premade but the place I got them from will alter them if they were purchased there. That is a GREAT idea and thanks for that. The valve is very restricted as you can see from the pic. I want to find a less restrictive one.
View attachment 576413

Based on that picture, I would definitely see if I could find a three-quarter inch valve. Have you by chance talked to Surplus Center to see what they would charge to ship it to Canada via USPS?

Aaron Z

 

[Hilbilly]

I think I found a local supplier of Prince valves but they are closed for the day. I will try them tomorrow.

Thinking the 1/2" valve would work since it is rated for the same flows and pressures.