Reducing flow and pressure in hydraulic branch circuit

[Chilly807]

So, having come full circle, we're back to a flow divider valve. They're about $100 each, I've been thinking about adding one to my 3 point circuit. The controlled flow is easily adjustable, excess gets returned to tank. Most if not all are pressure compensated so you get the same flow regardless of operating pressure.

This is the same kind of thing you find on log loaders, boom trucks, etc. The flow rate for the main lift cylinders is way too fast for the bucket positioning cylinder, so they reduce it to a workable safe level by using flow dividers.

I think the valve would be okay with a two-stage pump, depending on what the change-over pressure is, since the main line pressure before the valve wouldn't be any higher than normal.

It may simply be a case of this is what it's going to take to accomplish what you want to do, unfortunately it's not a cheap solution, and if this is the valve Prince has back-ordered, it's not going to be a quick one either.

You can use only one assuming you have a separate branch circuit (two-spool valve = one spool for log lift, the other for knife position). If the cylinders on those two accessory branches are sized right, the same flow rate should work well for each of them. The rest of the circuit (main valve and cylinder for splitting) will have full flow available.

Sean

 

[Scooby074]

So, having come full circle, we're back to a flow divider valve.
Sean

Yes funny about that:thumbsup::laughing:

But, a flow divider will continuously dump its 2 GPM (or whatever its set at) back to tank through the aux circuit regardless if the circuit is used or not, correct?

That means losing 2 GPM from the split circuit and an increase (somewhat minor) in cycle time. Not bad at low pressure (22gpm) but at high pressure (7gpm) it might be noticed.

The idea of using the PB off the 2 spool and restrictors at the cylinders was to have the full pump flow available to the split circuit. Flow to the split cylinder would only be reduced during cycling of the aux cylinders.

At high pressure (7gpm to split cylinder) cylinder extension time is 17.1s

At high pressure with 2gpm flow divider (5gpm to split cyl) cylinder extend time is 24s

I understand that the cyl wont be at high press for the full stroke (maybe 1/2 ) but this is a worse case scenario.


Sean, see the attachment. I believe this is the circuit as you recommend, with the flow divider

 

[glastron23]

Scooby, what we are missing is that just because we have 22 gpm at the valve does not mean we have to use all of it, i would install 2 of the Sun cartridges on the cylinder and try not to pull the valve full open.
if you do the PR will handle the over pressure on the system, yes not the prefect design but just remember that the rest of the system (splitting) will make the PR to work a heck of a lot more than the lift.
The amount of time that log lift will be used is minimal compared to the time the splitter cylinder will be at max PSI.
Just because the PR is set for 2500 psi does not mean that it is closed all the time until the system hits 2600 psi. the valve has a cracking pressure a lot lower than 2500 Jim

 

[Scooby074]

Scooby, what we are missing is that just because we have 22 gpm at the valve does not mean we have to use all of it, i would install 2 of the Sun cartridges on the cylinder and try not to pull the valve full open.
if you do the PR will handle the over pressure on the system, yes not the prefect design but just remember that the rest of the system (splitting) will make the PR to work a heck of a lot more than the lift.
The amount of time that log lift will be used is minimal compared to the time the splitter cylinder will be at max PSI.
Just because the PR is set for 2500 psi does not mean that it is closed all the time until the system hits 2600 psi. the valve has a cracking pressure a lot lower than 2500 Jim

The sun cartage has the same function as the Buyers throttle valve you linked to earlier right? The buyers might be easier to find and cheaper as i think the sun valve needs a block to mount which is extra cost.

The check while reducing the potential for a spike on retraction, causes me an additional problem of no flow control during retract.

Restrictor orifices give me reduced flow in both directions with a single orifice per circuit. Plus its way cheaper. As mentioned i dont believe ill need any further adjustment to flow once i have one that's satisfactory. Four restrictors with checks (one /port / cylinder) would be ideal but $$

Assuming i went with a restrictor, were my calculations correct regarding any spike in pressure on the base side of the piston during retract? If im right, instead of a pressure increase, id end up with a pressure reduction. ieressure on The Smaller area of the rod side being applied to the larger area of the base side of the piston.

 

[slowzuki]

Your diameter calc is not correct, you need to solve for 2 gpm at the relief valve pressure because you are wanting 2 gpm at relief pressure. Your delta P is essentially the relief valve pressure as your load is so low. I can't tell you much about your formula, there should be a temperature component to it. As temp goes up, so will the flow to the lift cylinder, so in cold weather it will lift slower until it is up to operating temp.

You may find you get a whine in the orifice too as it will be a very high speed jet of oil.

RE your last post, last paragraph, not sure what you mean. Is the lift single acting with the single orifice at the cylinder with gravity return? It will take forever to return if so as your delta P going back to the tank will only be maybe a psi. If you are power returning and orifice at the base, the orifice will do the same job on the oil trying to leave the cylinder, but like you said, the pressure will be lower by the ratio of piston area so your return speed will also be slower.

 

[Chilly807]

The configuration I had in mind was the flow divider placed after the splitter valve, and before the 2-spool valve for the wedge cylinder and log lift. You'd have full flow available at all times to the splitter valve, and reduced flow going to the 2 spool valve for the log lift and wedge.

The Prince logsplitter valves list a maximum tank port pressure of 500 psi. With the load you'd have with a typical log lift or wedge cylinder, you should be below this.

The alternative is a different type of splitter valve that incorporates a power beyond option, if such a thing is available, or simply a detented single spool valve with a mechanical knock-off mechanism.

Sean

Yes funny about that:thumbsup::laughing:

But, a flow divider will continuously dump its 2 GPM (or whatever its set at) back to tank through the aux circuit regardless if the circuit is used or not, correct?

That means losing 2 GPM from the split circuit and an increase (somewhat minor) in cycle time. Not bad at low pressure (22gpm) but at high pressure (7gpm) it might be noticed.

The idea of using the PB off the 2 spool and restrictors at the cylinders was to have the full pump flow available to the split circuit. Flow to the split cylinder would only be reduced during cycling of the aux cylinders.

At high pressure (7gpm to split cylinder) cylinder extension time is 17.1s

At high pressure with 2gpm flow divider (5gpm to split cyl) cylinder extend time is 24s

I understand that the cyl wont be at high press for the full stroke (maybe 1/2 ) but this is a worse case scenario.


Sean, see the attachment. I believe this is the circuit as you recommend, with the flow divider

 

[Scooby074]

Your diameter calc is not correct, you need to solve for 2 gpm at the relief valve pressure because you are wanting 2 gpm at relief pressure. Your delta P is essentially the relief valve pressure as your load is so low. I can't tell you much about your formula, there should be a temperature component to it. As temp goes up, so will the flow to the lift cylinder, so in cold weather it will lift slower until it is up to operating temp.

You may find you get a whine in the orifice too as it will be a very high speed jet of oil.

RE your last post, last paragraph, not sure what you mean. Is the lift single acting with the single orifice at the cylinder with gravity return? It will take forever to return if so as your delta P going back to the tank will only be maybe a psi. If you are power returning and orifice at the base, the orifice will do the same job on the oil trying to leave the cylinder, but like you said, the pressure will be lower by the ratio of piston area so your return speed will also be slower.

I thought i did solve for 2gpm (Q) in that orifice formula? I admit there is a lot missing from it, like fluid viscosity and delta T. Ill try and find a more complete formula.
I also screwed up my Delta P. Ill redo.


Yes the cylinder will be double acting. Even slower on the return is a good thing so the log lift wont slam into the ground

The configuration I had in mind was the flow divider placed after the splitter valve, and before the 2-spool valve for the wedge cylinder and log lift. You'd have full flow available at all times to the splitter valve, and reduced flow going to the 2 spool valve for the log lift and wedge.

The Prince logsplitter valves list a maximum tank port pressure of 500 psi. With the load you'd have with a typical log lift or wedge cylinder, you should be below this.

The alternative is a different type of splitter valve that incorporates a power beyond option, if such a thing is available, or simply a detented single spool valve with a mechanical knock-off mechanism.

Sean

Sean, PB on the splitter valve is the perfect solution.... While prince makes one its not available in stock. I got the Auto Cycle valve at princess for a good price (sale) so im stuck with making it work.

The only valve i got with PB as an option is the 2 spool. I really dont want to use the tank port on the splitter valve to power the 2 spool. Doing damage to a $300 splitter valve wouldnt be a good day. I havent calculated the pressure ill see on the lift cyl, but i imagine its higher than 500psi. The lift is 45* to the ground and the cylinder maybe 40-42? so there is a fair bit of inline push there and the corresponding pressure could be high.

 

[Scooby074]

This page looks "fun" for orifice calculations:

How to do an orifice calculation - Chemical engineering other topics FAQ - Eng-Tips

 

[glastron23]

Scooby, i've been running some scenario's through the limited program i have. What is really screwing with the numbers is the 22gpm/7 gpm. When the system starts to work the pump is in HVLP (22gpm) as soon as the orifice kicks in then the pump pressure rises causing it to go to LVHP (7gpm) there for dropping the cylinder speed and then the pressure at the cylinder!!
Man what a mess it's causing, I've tried to install a PR valve after the splitter valve and then plumb the lift control valve, setting this PR at 1000psi, it settles the system down a lot, the 22/7 is still messing with the numbers when the orifice is installed but it's a lot better.
As far as the 500 psi max pressure at the tank line of the splitter valve, this is for the internal PR and the kick out circuit of the valve as you need to add the back pressure PSI to any PR valves settings to get your correct working pressures. No need to worry about it as you will not be running both valves at the same time anyway.

 

[Scooby074]

Scooby, i've been running some scenario's through the limited program i have. What is really screwing with the numbers is the 22gpm/7 gpm. When the system starts to work the pump is in HVLP (22gpm) as soon as the orifice kicks in then the pump pressure rises causing it to go to LVHP (7gpm) there for dropping the cylinder speed and then the pressure at the cylinder!!
Man what a mess it's causing, I've tried to install a PR valve after the splitter valve and then plumb the lift control valve, setting this PR at 1000psi, it settles the system down a lot, the 22/7 is still messing with the numbers when the orifice is installed but it's a lot better.
As far as the 500 psi max pressure at the tank line of the splitter valve, this is for the internal PR and the kick out circuit of the valve as you need to add the back pressure PSI to any PR valves settings to get your correct working pressures. No need to worry about it as you will not be running both valves at the same time anyway.

Glastron, thanks for running the sim. Ive been trying to find a copy of FluidSim to download but cant find the hydraulic version. What your experiencing with the pump shifting was what i was scared of. Its kind of why i wanted the priority flow from the beginning.

I hope to get hoses tomorrow, as of right now i intend on going with orifices. If they dont work, im going to revisit it. I hope to be able to pick the brains of some hydraulic gurus tomorrow and ask their opinions as well.

If anybody is looking for hose, Alfagomma's hose is very competitively priced. Its actually about the same as Princess's Ryco hose. I think im going to go with Alfa's. Alfa's hose is $2.23/ft for 1/2 and $3.66 for 3/4 vs. Princess at $2.09 and $3.59 respectively.

FYI the splitter build thread is here: http://www.tractorbynet.com/forums/build-yourself/219145-woodsplitter-build-timberwolf-clone.html