Is a Cross Over Relief Valve Important

glastron23 · Oct 18, 2014

here's our plow truck.... and YES it has cross over reliefs.....

BAP · Oct 19, 2014

I can see the benefit of the cross over relief valve, particularly if you plow driving like Mario Andretti, which a lot of people do. Plowing slow, with a tractor is different than a pickup plowing at 20-30 mph. The reason I asked, was that several of the companies that sell plows for tractors, do not put them on as standard equipment. That got me to thinking as to whether or not there was a need for one or of it is overkill.

glastron23 · Oct 19, 2014

BAP, yes the tractor is not moving as fast, but hitting a solid curb will do the same damage, trying to stop 1 1/2 or 2 tons of steel will bend crap. $150.00 is cheap insurance .

PILOON · Oct 20, 2014

I did a fair amount of private drive plowing in a very rugged rocky environment with a 3/4 ton GMC.
The only time I tripped the crossover was when I'd try to use rt frt plow corner to pull icy snow banks away from something.
In fact it generally tripped whenever I did not want it to. On the other hand the trip mechanism did work often due to lots of protruding rocks and stumps.

I have had 3 plow trucks and on my 4th tractor and am very comfortable without a crossover on my tractor*, however I'd never plow w/o a trip mechanism of some sort. (*and I have a couple of crossover valves in my inventory)

BAP · Oct 20, 2014

Yea, I have done a lot of off road plowing with Fisher and Diamond plows. Used them on GM pickups when I used to farm plowing out roads in fields during winter to haul out manure to pile in field. Also plowed some rough roadways and driveways that were dirt and particularly in the spring after they have thawed, rutted and refrozen. I don't believe I ever had a relief valve trip. The trip cutting edges would trip first. I would never run a plow that didn't have a trip cutting edge. They are an absolute must for rough terrain plowing.
.

avc8130 · Oct 20, 2014

I've had my crossover relief trip a few times on my truck that I was aware of.

One time it actually tripped too slowly and I blew an angle hose that had rubbed a bit and was weak.

Another time was when a Pontiac drove straight into my plow at ~50 mph. The plow wound up a bit tweaked, but no damage to the truck. I was stationary at the time about to re-enter my own driveway clearing up near the road. This could have easily happened with the tractor.

ac

J_J · Oct 21, 2014

Technically, you probably need a crossover relief valve, as the tractor can strike an object with enough force to generate a hyd spike strong enough to do some damage.

Cheap insurance.

LD1 · Oct 21, 2014

Lots of questions recently about plows and crv's in recent days. Yep winter is coming.

IMO, YES a CRV is necessary.

Think about how a little bottle jack works. You have a little plunger hooked to a pivot and a lever. Move the lever and you can generate an awful lot of pressure (~10000psi) with the plunger without much force on the lever.

A plow is basically the same thing. You have the plow angled, the extended edge is the lever/handle, and the cylinder becomes the plunger.

Most plow cylinders are 1.5" diameter. Which has an area of ~1.76" sq.

The cylinders are typically ~8" from the central pivot. So on a 7' plow you would have 5.25:1 mechanical advantage.

So for every 1lb of force you put on the edge of the plow, you are putting 5.25# of force on the piston, which transfers to about 3psi.

So given that most the cylinders are rated for 2500psi, as are the hoses, if you push with mroe than 833# of force on the edge of the plow, you are exceeding 2500psi in the cylinder and hoses and risk damage.

SO, bottom line, it dont take much force or much speed to exceed the rated pressure inside the system if you have an unbalanced load in front of the plow, or hit something. Wider plows more so.

jambx · Oct 23, 2014

Great info - but I do have a request;

I would like to find a cross-over relief valve that has ¼ NPT ports (since that is what I am using for my build) and don't want to use reducers if at all possible.

is there any chance someone can direction me to Cross Over valve that use 1/4 NPT direct fittings?

Also, if I am going to get a unit (like the one depicted here from Surplus Center) I assume it is pre-set to 3000 PSI so how does one determine where it should be set for their specific requirement (and from what I read here 2500+ is where it needs to be). Should I just leave it at 3000 or if it has to come down and how does one know where exactly to set it?

1/2 NPT 30 GPM 1500-3000 PSI HYD CUSHION VALVE

Any clarity is greatly appreciated,

Jim

mikehaugen · Oct 23, 2014

jambx said:
Great info - but I do have a request;

I would like to find a cross-over relief valve that has ¼ NPT ports (since that is what I am using for my build) and don't want to use reducers if at all possible.

is there any chance someone can direction me to Cross Over valve that use 1/4 NPT direct fittings?

Also, if I am going to get a unit (like the one depicted here from Surplus Center) I assume it is pre-set to 3000 PSI so how does one determine where it should be set for their specific requirement (and from what I read here 2500+ is where it needs to be). Should I just leave it at 3000 or if it has to come down and how does one know where exactly to set it?

1/2 NPT 30 GPM 1500-3000 PSI HYD CUSHION VALVE

Any clarity is greatly appreciated,

Jim