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Construction Equipment trailer brakes

Construction Equipment trailer brakes

Construction Equipment trailer brakes

Working on some construction equipment. Basically, a 6 wheel drive dump truck with the bed taken off, and a giant gooseneck trailer hooked to it. Still in setup stages.

The truck has hydraulic brakes that operate on 0 to 1300 psi.

The image is of the trucks service brake valve. A1 and A2 are two separate brake ports, for brakes on two separate axles. A1 and A2 have a maximum output setting of 1300 psi, with the brake fully applied. P1 and P2 are from the same pump source. If curiosity needs to know why there is P1 and P2 from one source, the source gets split by an inverse shuttle valve to keep the circuits separate(safety?).

The trailer has hydraulic brakes that require 1800 psi.

Assume that there is another, separate, source of oil flow on the truck which will provide 1800 psi when activated.

Is there any sort of valve that would allow me to use the 0 to 1300 psi from the trucks service brakes, to operate a pilot valve to control the trailers brake in proportion @ 0 to 1800psi? A normal pilot operated spool valve will not work- there would be no variability in the 1800 psi circuit, the brakes are a single acting, spring released circuit. The valve also needs to drain the brake work port to the trailer when it is not activated.

In effect, what I need is the same hydraulic function of the truck's service brake valve, but using 0-1300psi pilot oil instead of a footpedal. Doable?

Think of this like a hydraulic version of a pickup truck electric brake controller..


RE: Construction Equipment trailer brakes

I'd be a little leery of modifying a braking system, especially on a commercial vehicle. Are there DOT regs on this?

That said, if you obtain an off-the-shelf hydraulic cylinder where the piston side is 38% larger area than the rod side (1800psi/1300psi = 1.38) and replace the seals with ones that are compatible with the fluid, then you could set up your system to apply 1300 psi to the piston side and obtain 1800 psi on the rod side. You would also need to add a normally-open, pilot-to-close logic valve into the loop to keep the system closed and full of hydraulic fluid while being able to release pressure and open up fully when your foot is off of the brake.

A hydraulic cylinder with a 2" bore and 1" rod is a 1.33 ratio, which would get you pretty darn close. At 1300psi in the truck, you would end up with 1733psi on the trailer.

It probably wouldn't be a bad idea to have a gauge on both sides of the system that can be read in the cab. Most importantly, though, you need to make sure that something like this would be legal to be used on public roads.

Engineering is not the science behind building. It is the science behind not building.

RE: Construction Equipment trailer brakes

Also... A normal hydraulic brake proportional valve exists for the purpose of reducing pressure to the rear brakes. Rear brake lockup and especially trailer brake lockup during heavy braking will cause the rear of the vehicle, along with the trailer, to switch places with the front of your vehicle... a very exciting experience. Are you sure that you need the full 1800 psi to the rear brakes?

Also... how will you connect/disconnect the brakes and purge all of the air out of them when you connect/disconnect the trailer?

Engineering is not the science behind building. It is the science behind not building.

RE: Construction Equipment trailer brakes


Off road trucks. They don't move fast, brake modifications very feasable and will not jeopardize the trucks safety. Also- the original truck brakes will not be changed at all, they will work as from factory. There are many older trucks set up to use these trailers, and use the aftermarket ECM that I mentioned, we are trying to find a way to get rid of some of the wiring and the control module. Originally, the module had an input for brake pressure on the truck, and supplied an output to the trailer brakes. The higher pressure was obtained from another pump on the machine using an accumulator/charging valve system and a load sensing pump.

Technically speaking, I have to find a way to get the full 1800 to the rear brakes, because it is specified. The cylinder with logic valve sounds like it would actually work quite well, but the customer wants to try and find a way to valve it. I'm not sure how well it would hold up in an earthmoving setting as well.

The hydraulic connections are simple hydraulic hoses and oring face fittings. There are bleeders on the brake calipers on the truck (LARGE calipers, not your daughters honda). Its also not difficult to bleed them along the way as there are several connections.

Just a little background- these trailers stay connected for months while being used, then they might sit for years in between, so connections are fairly "permanent" , as you would say.

What I have scribbled down so far is a charging circuit with accumulators (load sensing function built in for LS pump) to supply this new 1800 psi brake circuit. It will cut in and out from 1800 to 2200. This new supply is sourced off a different pump on the machine than the truck brakes. I plan on having a pressure reducing valve after the charging valve/accumulators to keep it at 1800 while in use. I just need a way to proportionally activate the higher pressure circuit with the lower pressure workport oil. Without an ecm and pressure sensors!

RE: Construction Equipment trailer brakes

You need a pilot-operated proportional pressure-reducing valve. (Note - not a pressure-relieving valve). Speak with your hydraulics rep. He should be able to recommend a valve that has the correct curve for this application.

Tie the accumulator to the input, the pilot line to the prime mover brake line and the output to the trailer brakes.

Engineering is not the science behind building. It is the science behind not building.

RE: Construction Equipment trailer brakes

See, I thought that's more or less what I needed. I have several calls out, one rep I talked to kept trying to tell me I needed a relief valve and not a reducing valve...

I will look elsewhere. Any knowledge off hand of a brand? It will have to have an adjustment on the pilot actuator to be sensitive to my 1300 psi.

Also- thanks for the quick and detailed responses!

RE: Construction Equipment trailer brakes

Interesting enough, I also found these just now. You got me going on the intensifer idea. It is really simple and self contained, which I like. See below link.


They reciprocate and have built in check valves, eliminating the need for any makeup oil. Logic is built in.

From what I can tell, there is no way to release the pressure though due to the two uppermost check valves (see schematic).

If I used some sort of normally open pilot operated valve that closes when I supply truck brake pressure, normally draining the TRAILER brake actuator. Use low pressure setting so that truck brake pressure can close off actuator drain, and allow intensifier to build pressure?

I also found these, they call them quick exhaust valves. https://www.bifold.co.uk/item/QEV150410S.aspx

Do you think this would work?

I attached a crude schematic I made of what I am thinking.

RE: Construction Equipment trailer brakes

I think that the Parker valve that you have will not be what you need. In many of the remote-pilot operated valves, the back pressure at the pilot port is directly additive to the pressure from the spring. I think that a proportional valve would be proportional, as opposed to additive. Additionally, I am not a huge fan of cartridge valves, unless you are very certain that your system will be clean. For me, this always meant additional filtration to the system over what comes from the factory. I have always had bad luck with the little screens inside of cartridge valves getting clogged up with debris. But my experience is in extremely dirty environments with hoses being disconnected and reconnected multiple times a day by careless operators (though who am I kidding - I probably wouldn't be any more careful than they are, were I in their shoes.)

Regarding lock-up of the circuit: You are correct that you would have to vent the lines somehow when there's no pressure on the truck's brake line. It appears that by design, the fluid is intended to only exit through the HP port and not intended to come back in... I think. I don't know exactly how the pilot-operated check valve (POV) is supposed to work in this, since there likely would not be large amounts of pressure on the return to tank line, but I would think that if there is enough pressure, it would open POV and allow reverse flow. That may be the reason that a directional valve is required - to keep back pressure on the tank port, which would open the pilot-operated check valve.

I'm not familiar with the quick-exhaust shuttle valve, but it seems like it could work.

Engineering is not the science behind building. It is the science behind not building.

RE: Construction Equipment trailer brakes

Engineer Tex-

I am backpedalling. I am looking at this way too complicated. I really like your idea with the 1.33 ratio cylinder. Simple.

I wanted to ask you this- I have shuttle valves and check valves on handI attached a crude drawing of what I am thinking. Check valve allows for makeup oil ("slack adjusting"), shuttle valve allows pressure to build, but pressure from brake to exhaust to reservoir when pressure is removed.

Am I thinking right, I am a little concerned about the operation of the shuttle ball though- do you think it would reliably relieve the brake to the reservoir consistently in the arrangement?

I want to make your suggestion work, it would make everything so much simpler. I am not against a pilot operated NO valve, but would like to see if this is possible with on hand and easy-to-get parts, I.E. down the road at local cat dealer instead of flying parts in next day air if repairs are needed.

Thanks again for all your help so far!


RE: Construction Equipment trailer brakes

I share your concern about the trailer brakes not relieving every single time. Especially with thermal expansion/contraction, I could easily see the trailer brakes getting locked up.

You could also use a N.O. cam follower valve and have it actuated closed by contact with the moving end of the cylinder rod. I would also make sure that this does not come in contact with the sealing surface of the rod, i.e., make sure the rod is long enough to keep from the sealing surface touching the cam follower. Though a cam follower may not be any more likely to be on hand in a remote location.

Engineering is not the science behind building. It is the science behind not building.

RE: Construction Equipment trailer brakes

Thanks for the replies! A little familiar with mico products. Not so much the others but good for reference.

Anyways, there are several solutions on the table now, waiting on them to decide what they want to do with it.

Thanks again!

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