Looking for hydraulic advice

[Fawteen]

I'm building a home-made dump trailer. I have a 3.7GPM self-contained piston pump/reservoir/valve being driven by a geared-down gas engine. After a little testing, it is immediately apparent that I need to seriously restrict the flow in the system. The pump with half-inch fittings is moving WAY too much fluid, even with the motor at an idle.
I'm aware of in-line restrictors and needle valves, but from what I can find on line, inline restrictors don't go down far enough flow-wise and tend to be one-way, needle valves are too expensive.

What I'd LIKE to do is make my own using a pipe plug and drilling an orifice in it. I can foresee two issues with this:

1. I have no idea what size to make the orifice, and;
2. Pipe plug material is probably too soft and will erode.

This is a bucks-down project, so the less money I have to spend the more likely it is to get done.

Details at the link.

Input?
Dump Trailer Project

 

[Chip812]

Hmmm... Wouldn't it be wiser to gear the engine down some more? (I don't know, just asking)...
 

[Fawteen]

Don't think so, I ran it at a dead idle and it still moves too much fluid.
 

[Puddles]

When I got my 3-point backhoe, the boom up and down was way too fast for me. A good buddy of mine who is a heavy equipment operator suggested I take a short piece of round stock that would fit in the hose connection and drill a small hole in the round stock. I did, and it works great!
 

[Fawteen]

Do you recall what size hole you used?
 

[Puddles]

All the fittings, and hoses are 1/4-inch, if I remember correctly I drilled a 3/32-inch hole in the round stock.


 

[Fawteen]

Thanks, I'll use that as a starting spot then.

Nice rig!
 

[Dick L]

An oriface like that would work. The size of the hole depends in how long of a land you leave in the plug.

My heavy backhoe trailer has an inline flow controll valve. It is set up so I can stand on the back and it will tip down to the ground. I can drive a dozer or backhoe up onto the trailer and sets down flat as the same speed it goes down with me standing on it. It is a little bitty valve with a needle control with a lock.
 

[J. Schwiebert]

You need to remember when you restrict the flow you build pressure on the inlet side. Next thing you need to think about is when you lower the trailer do you want to be able to adjust the rate of drop. Me I would also gear it down more. Must be a Williams unit. J.
 

[Dick L]

Might Try Granger
Slow down flow. Or her sister

 

[Dick L]

and use a bypass flow control.
Click : D

 

[NCWayne]

Couple of questions. First how large is the oil tank your using? Second, how long do you intend to leave the system in operation after you start the engine?
Reasons I ask are this. Dumping oil dumping off through an orfice, relief valve, etc means that the oil isn't doing any work. That being the case all the restriction does is create heat in the system. It doesn't take long dumping even a gallon a minute off to create ALOT of heat in a hydraulic system. If the tank doesn't hold enough volume for the oil to hang around and cool off before being circulated across the restriction over, and over, and over again within a short period of time, the heat will accumulate even faster. Ultimately you'll overheat the system to the degree that it will break down the additives in the oil, and cause premature pump failure, seal failure in the cylinder, etc. Typically the rule is that you want a tank with a capacity at least twice the volume being pumped. In your case, with such a small pump/system to start with, it would really need to be a bit larger to prevent the chance of overheating if you plan to leave the engine running for any length of time.

That said the right way to do what your wanting is to install a simple flow control valve in the system. Doing this will make the full flow from the pump usable, but also allow you to properly meter the needed flow and allow the excess flow to return to the tank. This will allow you to run the engine at a higher speed, which will give it the necessary HP, and some cushion in that department (ie-allow the governor to work properly), to handle the heaviest loads (ie-the highest required system pressures), and not lug, or stall the engine, or slow down the flow as a result of said lugging or stalling. In other words the valve will allow the same GPM across it at 1500 psi as it will at 3000 psi while the flow across a true, fixed orifice size will usually vary with the pressure. Also the valve in the link below has a relief valve integrated into it so even if it were to get shut completely the pump wouldn't dead head and be damaged as a result. With a small, fixed orifice, the chance of dead heading the pump due to a piece of trash in the system could create a potentially hazardous situation given that piston pumps are considered to be positive diaplacement, and many are capabile of pressures into the 6000 psi range. If you have a relief already in the system that wouldn't be an issue, if not it's something to think about.

Good luck and post some pics so we can see the setup when your done with it.
Flow Control at Northern Tool

 

[Fawteen]

Yup on the Williams.

The integral valve is double-acting. Based on my limited knowledge of hydraulics, I'm thinking the it is an open center valve as the pump can idle with the valve in the center position. If that's the case, then pressure/heat problems will only surface during actual movement of the piston, IE long enough to raise and lower the bed.

Unless I'm missing something (and I probably am...) I don't see this as a problem.

I'm building this out of whatever I have laying around from years of being a packrat. If it were being purpose-built, I've used a shorter stroke cylinder and a smaller pump.

Not knowing what I was doing, I was worried about turning the pump fast enough. Obviously, that's not going to be a problem. I'll swap the smaller gear onto the engine and scrounge around and see what I can find for a larger gear for the pump.

I also have a friend digging through his stash thinking he may have a flow control valve somewhere.
 

[Fawteen]

Wayne, see my reply to Mr. Schwiebert below. It's a self-contained Williams unit, about a 2 gallon tank, less the volume the pump assembly takes up.

Also, I'm pretty sure it's an open-center valve, so the pump is just recirculating oil through the valve unless you're actually raising/lowering the bed.

I don't see heat buildup being a problem, especially since it will see very occasional use.
 

[Jim in Ma.]

I have used a water gate valve to restrict the flow too.