Looking for hydraulic advice

Fawteen

Well-known Member
Location
Downeast Maine

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

12570.jpg
 
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.
 
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.
 
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
 
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.
 
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.
 
Slow the pump down.
I built a dump trailer out of the back half of an old F350 about 15 years ago. Used a 5 hp Techumseh hooked up to the original pump under the dump trailer. My problem was the the engine didn't have enough oomph to lift the bed if it was loaded heavy.
What I did is added a jack shaft made up of sprockets, etc from an old snow blower. It slowed the pump down by about 2/3rds and worked real good after that.
You could accomplish your goal by adding a jack shaft
 
I think you're getting a lot more than 3.7 GPM. I thought Williams pumps like that only ran about 1000 RPM max? Looking at your picture, I think you need to put a much larger sprocket on the pump to slow it down. The way you have it with a smaller pulley, you're speeding it up. A smaller hole for the oil to go through may put excessive back pressure on the system and cause damage. Another option might be a priority flow divider that you could just divert excess flow back to the tank.
 
I've been following your progress on your trailer. I agree with the others who thought the pump speed being too fast is your problem. I've got an 8HP Briggs running a truck pump, and I used the biggest and the smallest sprockets that the local farm store stocked. #40 chain. Little sprocket on the engine. Dump speed seems to be about normal. Here's a pic showing the sprockets.
a91464.jpg
 
You mentioned an engine house over on the shop forum. My Daughter-in-law was throwing an old storage tub away, and it fits perfectly over the engine on our trailer. Even new - they're pretty cheap.
a91466.jpg
 
OK, looked at the pics, and read everything. Making some assumptiuons here about the pump in that the actual 3.7 GPM rating is at 1000 RPM. making those assumptions here's my next observations and suggestions.

Looking at the pic you've got the sprocket sizes backwards (ie the larger one on the engine and the smaller on the pump) so your actually speeding up the pump. That said I'd think you'd want to run the engine well above an idle so it has power to dump the trailer when it's loaded and the highest hydraulic pressure is needed. To do that requires nothing more than some simple math. If you want to run the engine at 2000 RPM and the pump at 1000 then you need two sprockets with one having twice as many teeth as the other. This would turn the pump at 1000 RPM and, assuming the 3.7 gallons is at 1000 RPM, would net you right at 3.7 gallons of flow.

Now, to slow the pump down, and reduce your flow, all you need to do is use spockets with an even larger tooth count difference. If you were to put a 25 tooth sprocket on the engine and a 5 tooth sprocket on the pump with the engine at 2000 RPM the pump would turn at one fifth of it's usual speed, or 200 RPM. This, in theory, would give you a pump flow of about .7 GPM. If that isn't enough flow you can go with say a 20 tooth sprocket and a 5 tooth sprocket. This would change to the ratio to 4-to-1 which would turn the pump at 250 RPM and give you a flow of .925 GPM. Using the 4 to one ratio if you sped the engine up to 3600 RPM than it would give you a pump speed of 900 RPM, and should give you a flow of about 3.33 GPM. By the same token with the engine at 2000 RPM it would also allow you to slow the engine down some and reduce the flow from the pump wto well under a gallon a minute.

That all said, for the cost of two sprockets you should be able to get your flow rate down low enough to meet your needs and still keep the engine at a high enough RPM for the engine to do it's job properly, and also give you wome wiggle room to control the flow with the throttle to nearly it's maximum. That's a close estimate on taking care of the problem using just two different sprickets. Beyond that you can play with sprocket sizes, if you want, to achieve the optimal engine speed and flow rate compatible with your needs.

Granted I understand your wanting to make the thing using all parts you have lying around, BTDT many times myself. Unfortunately there are times when it is cheaper and easier to buy the critical parts needed to make the thing RIGHT, than it is to use will fit parts and then have to buy another, more expensive part, to make sure the will fits actually do fit. Good luck.
 
Well, yes, but...

The engine has an integral gearbox that produces 650 RPM at WOT. Not having any experience to go by, I was concerned about being able to turn the pump at it's rated speed of 1000 RPM, so I went with an 18 on the engine and a 12 on the pump, which according to my math should turn the pump at 975 with the engine at WOT.

Obviously, that's MUCH too fast, but even with the engine at idle (I haven't put my tach on it to see what that is) it's too much flow.

I will be re-gearing, but I have another solution in mind that I'm going to try this morning. If it works, I'll post the details.
 
Use either a globe valve or a ball valve to throttle flow, NEVER a gate valve. A gate fits loose in the valve body and should be either fully open or totally closed, nowhere in between.. From an old pipefitter)
 
Sorry Fawteen - I failed to read that your engine had a gear reduction.

Paul
 
You DO NOT want the restrict the flow. That will lead to heat buildup. You will cook your fluid in no time.

Remember hydraulic fluid is incompressible. By restricting it, you are making the pump work to get the fluid to flow through. Work has to be accounted for somehow, and that will end up being as heat.

You need to bypass or divert the excess flow.

Cliff(VA)
 
Yup, came to that conclusion based on all the feedback.

See the "Hydraulic Problem Solved" post for the solution I came up with after a lot of advice from various sources.

Wunnerful thing, the innerwebz..."8^)
 

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