Pressure Relief Block, Curtis plow

[SpudHauler]

Is a pressure relief block like this one pictured here required when using a 12v selector valve?
Or does the selector valve, from Surplus Center, have it's own release?
I bent one of my bolts holding the swing cylinders and am wondering if it was because i did not re-install the relief block when I installed the selector valve.
The selector valve gives me the up/down and left/right using one spool on my RTV1100 Kubota.
Third picture is how it is connected out front and on the spool lever I have a push button switch for the left/right cylinder activation.

 

[J_J]

Can't see the whole valve, but I don't believe the selector valve has a relief. The relief would come from the FEL valve.

Is the one you have?

https://www.surpluscenter.com/item.asp?item=9-7852&catname=hydraulic

 

[kennyd]

Spud, you still need the cushion valve AKA cross-over relief valve. Your solenoid valve blocks both work ports when it's in neutral so the fluid would have nowhere to go.

 

[RickB]

Spud, you still need the cushion valve AKA cross-over relief valve. Your solenoid valve blocks both work ports when it's in neutral so the fluid would have nowhere to go.

Correct answer.

 

[J_J]

It is optional to use a relief valve with cylinders in your situation. They are designed to relieve load generated pressure. If you choose to use the relief valve to protect the cylinders, then you should use a [ DRV ] Dual relief valve. If you go the full route, then you need a DRV for each cyl. You should set the relief pressure about 50 to 100 psi lower than the FEL relief valve.

They need to be close to the cyl for full protection. They usually come set for abut 2000 psi, so use a hyd gage to adjust.

 

[SpudHauler]

Yes JJ that is the 12v selector valve from Surplus Centre you linked to that I am using.
So you do need the cross-over relief because the selector valve blocks the circuit. And your spool valve would never get the chance to go to relief mode. That is if the spool valve can relieve pressure from a bump like one on a plow blade.
I caught an edge with the plow at some point and bent just the bolt. Lucky.
In changing my plow mount I found the bent bolt and want to prevent that if I can.
So the relief dumps the pressure back to the other cylinder in this case and allows some movement of the blade instead of allowing things to get bent. Cool.
And I just thought it was for making connections. You learn lots from this site, thanks to you guys.:thumbsup:

 

[J_J]

The quality of the bolt might have something to do with the bend.

You can get manifolds for many types of functions. Simple to elaborate.

A1 Manifold Supply - Browse our Catalog of Aluminum Distribution, Pneumatic and Hydraulic Manifolds

http://www.datum-manifolds.com/pages/Products.html

 

[RickB]

It is optional to use a relief valve with cylinders in your situation. They are designed to relieve load generated pressure. If you choose to use the relief valve to protect the cylinders, then you should use a [ DRV ] Dual relief valve. If you go the full route, then you need a DRV for each cyl. You should set the relief pressure about 50 to 100 psi lower than the FEL relief valve.

They need to be close to the cyl for full protection. They usually come set for abut 2000 psi, so use a hyd gage to adjust.

Kinda hard to have a DRV for each of two single acting cylinders. The pictured valve is designed and sold to protect both with a single block, hence the name 'crossover relief'.
Circuit relief protection is set above system relief pressure, not at or below. Setting circuit relief pressure below system pressure lowers system pressure by default, and is a mistake best not made.
Crossover relief valving is optional on a snowplow power angle circuit only to the extent the owner is willing to sacrifice a hose, valve body or cylinder when severe shock loading is applied to the plow and angle circuit components. The OP's results are proof and typical. Having a crossover valve bought, paid for and not installed on a plow's angle circuit is somewhere between risky and downright foolish.

 

[J_J]

When do you ever set a downstream relief valve higher than system pressure?

 

[RickB]

When do you ever set a downstream relief valve higher than system pressure?

Every single time that the RV is protecting a work circuit from shock loading when the spool is centered and the work ports are isolated. Backhoes, snowplows, whatever. If nominal system pressure is 2500 psi or so, circuit relief valves are typically 2750 -3000 psi.

 

[J_J]

SpudHauler, Are you using SA cyl, and if you did, did the B port go to tank? Do you have pic of your cyl?

 

[glastron23]

RickB totally agree, this circuit needs protection from induced pressures (fetching the blade on a big rock) some thing has to give, he got lucky and it was the bolts and not something REALLY expensive. JJ a relief to protect a cylinder needs to be higher, it's only function is to protect the cylinder/arms/hoses/valve body etc from induced load shocks and not to relieve the system pressures when in use.

 

[AKKAMAAN]

When do you ever set a downstream relief valve higher than system pressure?

This is for work port pressure relief valves....

When you want to prevent a function from "folding" from external force that creates higher pressure than pump pressure....

Example:

1>Knuckle boom crane, boom cylinder will drop when stick extends the length of the entire arm

2> steering cylinder on logging equipment, cant allow "folding" when you drive into a stump etc...that would jack knife the machine...


edit!
System PRV and work port PRV are protecting two separate parts of the system....separated by the spool valve (CV)....

I was once taught that the system PRV was a PUMP PROTECTION and the work port prv was a MOTOR/CYLINDER PROTECTION....I still like to express it that way...

Sometimes the structure can hold higher forces than pump can create, and a plow blade could eventually be a perfect example of that....

 

[RickB]

SpudHauler, Are you using SA cyl, and if you did, did the B port go to tank? Do you have pic of your cyl?

Snowplow angle cylinders don't have 'B' ports. The posted photo shows two cylinders with a single hose each. The butt end of the rod is the effective piston area. The rod seal is the only sealing element.

 

[J_J]

Every single time that the RV is protecting a work circuit from shock loading when the spool is centered and the work ports are isolated. Backhoes, snowplows, whatever. If nominal system pressure is 2500 psi or so, circuit relief valves are typically 2750 -3000 psi.

If the work ports are blocked, then you could set the relief pressure anywhere. What if the cyl are 2500 psi cyl?

 

[kennyd]

Thanks Rick, at least we understand how they work-hopefully Spud does now also:thumbsup:

 

[Duffster]

SpudHauler, Are you using SA cyl, ?

Did you look at the pics?

 

[J_J]

I do understand work port relief, and shock load. I am still looking at the selector valve, and the number of hoses attached.

 

[J_J]

Did you look at the pics?

Apparently I did not see that pic. Was it there at the start of the post?

Getting old sucks.

 

[RickB]

If the work ports are blocked, then you could set the relief pressure anywhere. What if the cyl are 2500 psi cyl?

If the system relief is 2500 PSI and the circuit relief is 2000 PSi, no more than 2000 psi can be applied to the cylinder in question. Components are supposed to be designed to withstand maximum system pressures. If the design calls for circuit relief @ 3000 psi those components better be chosen to handle it.

Give it up. You are wrong on this. I'm not going to sit here all night and debate with you. Guys from Jacksonville, FL need to be careful handing out snowplow advise. Some of us know a little more about the subject.