Power Trac 418 Tire fell off!!!

[J_J]

Short answer, yes.

What the relief does is to dump fluid to tank to keep the pump under a safe psi limit.

If something like a QD should pop off, or you grab a heavy load after the valve PB has passed the fluid downstream, the valve relief will try and relieve the circuit psi limit.

The pump is going to try and pump until something blows up or out. You should hear the relief valve whining.

The engine will also respond by trying to keep the HP up required to run all the hyd. The engine may slow down or stall.

Your relief valve should be just after the pump and before or at the first valve in an open center hyd system to protect anything in the series path.

Each valve in the series path can have it's own relief valve, and even be set differently to protect hyd controlled by the valve.

Usually, good practice is to set all the reliefs the same psi.

The relief psi setting is what limits the power of the hyd circuit.

If your hyd system seems less than ideal, a pressure test will tell you if the setting is still in specs.

A better test of your hyd system is using a pressure gage in conjunction with a flow meter and needle valve to determine the pumps potential to produce the advertised flow in GPM's.

 

[SpringHollow]

Hi JJ,

I understand most or all of what you said but that is all about protecting before the valve (protecting the pump) or limiting the pressure that gets sent to the circuit after the valve. But what if you lift up your loader arms in the cool morning, turn off the tractor, then the sun comes out and beats on the black hoses etc. The pressure will increase in proportion to the temperature. Or what if you are driving along with a heavy load and you hit a bump making the bucket bounce up and down creating a shock load. My understanding was that they liked a leaky valve because it protected the system from things like that. They were relying upon their pressure reliefs to protect the pump and attachments as you mentioned.

So having said that, I personally have never had any hydraulic failures on any of my cuts where the loader arms would easily stay up for a day or more. So if that is the reason they use leaky valves, I doubt it is necessary unless those cuts had some extra protection in their valve packages that I am not aware of. And if they did, the marginal increase in cost seems like it would be worth it.

If it is, as someone else suggested, to protect people from a load left up, in my opinion it is much more hazardous to have to constantly adjust your height.

I have needle valves installed so I can lock my loader arms when necessary but then I need to get off the tractor to change that height.

My hydraulic system is working fine but at some point I want to rebuild some of the cylinders.

Ken

 

[J_J]

I have only heard that leaky valve thing from only one person. Several are repeating it from him.

For people that want protection from shock loads, then a relief valve across the cyl is appropriate.

A lot of industrial equipment have them.

I haven't seen any figures of pressure with attachments sitting in the sun, but it is probably not much.

It does not take much to hold a QD tight.

Bottom line is , if I had purchasing a a PT with a non leaky valve setup or a Pt with a leaky valve, I would choose the non leak valve PT just because of logic alone..

You can bet they don't put that in their specs. [ We only use leaky valves because ] Yea sure.

Would anyone have the balls to tell a customer, choose this model because it has the most leaky valve we have ever used. This is a new standard for the industry.

Would leaky brakes enhance your decision to buy that model whatever?

 

[Marks481]

I haven't seen any figures of pressure with attachments sitting in the sun, but it is probably not much.

I hope not, since mine sit in the sun all the time, and I never worry about that.

I think this is the case where PT claims an unplanned side effect of component choice as a "deliberate design feature" to avoid criticism.

That being said, my lift arms take >30 minutes to lower (unless a heavy load is sitting on them), and it has never caused me any problems or concern. I have no idea how long it actually takes to drift down, I just know it will eventually.

 

[J_J]

The pressure buildup test would not be hard to do.

Just take a pressure gage and install the correct QD on it, and plug both hoses into the gage assembly when cold.

I sure wish I had a test bench and the software that Casey is using in his demos.

lsmith29530

I really did not mean to get off subject here. Sorry about your wheel rim.

I was born in Manning SC,

Lived in Dillon and Clinton, SC until i joined the Navy in 1960.

 

[SpringHollow]

For water in a rigid system, the rule of thumb is 100 psi per 1°F change in temperature - that is significant. The hoses probably expand slightly which would lessen the effect a little and obviously so will any leakage. The biggest effect I personally see is from cooling where a negative pressure (vacuum) is created.

Ken

 

[Marks481]

For water in a rigid system, the rule of thumb is 100 psi per ｰF change in temperature - that is significant.

So assuming your implement is depressurized when you disconnect it, that means it could handle 10F temp change before you hit operational pressure limit, maybe 15F before you blow a seal. Since my implements stay in the sun a lot, and that has never happened...

If the implement was already at 180F due to hot oil when you disconnected it, it would cool rapidly and draw a vacuum, and the subsequent heat up would have no effect.

On the lift arms, assuming you parked it in the sun, thermal expansion will only lift the arms a small amount; movement of the lift arms will relieve the pressure, probably with only a slight imperceptible lift of the arms.

 

[SpringHollow]

The post got messed up - i had typed 1 degree. I do see the vacuum - sucks in the flat face connector end. That usually happens fairly quickly.

Like I said earlier - I have never had a problem with valves that did not leak so I personally do not think it is an issue. But then I am not an engineer working for a company that might be worried about liability so easy for me to say.

Ken