Flow Divder/combiner or not??? Help!! 1

[hydrometer]

Hi Hydrometer here,my first time on this forum.
I have a question a client put to me.

He has an old Isuzu truck with PTO, PUMP and 2 Winches hooked up to it.

PTO pump currently puts out about 40lts per/min.
Winch(s) motor(s) require about 20 l/m.
Pressure line is "Teed" off to feed both winches at the same time. Both have their own control valve and can be used together or by themselves.

When being used together the customer requires BOTH winches pull 2 seperate items (load) at the same time and at the same speed.

I spoke to the manufacturer who said ,"just put on a bigger pump and this will give more flow to both winches which in turn will make them pull at the same time".

I sugested a flow divider / combiner, on the pressure line feeding both C/Vs. He said it didn't need one because a bigger pump would rectify the problem of one winch being faster than the other.

This didn't seem right to me, though flow will make it go, it won't make them run in sync with each other; especially under load.

The design does not allow a lot of room to add new things that's why I thought of putting a divider onto the pressure feed line.

Question?, would this work and would this be the correct way of getting both winches to work in unison when the customer requires the need to work both together (though they don't always work together - I belive they only need to work in unison in 1 direction only, though it wouldn't matter if they worked in both directions in unison)

The existing pump is quite old and would be working to it's maximum flow. It would be replaced by a pump with a flow rate of around 80l/m at 1200rpm.

I hope this is easy to understand and would be thankful for any help

thanks
Hydrometer

 

[hydromech]

Hydrometer...

One pump driving two winches will work, but only if the load is the same on both winches. If the load drops off on one of the winches, it will speed up and the other heavily loaded winch will slow down or stop.

A flow divider is the best option, how the winches work depends on exactly where you put the flow divider.

I won't go into the details now, but it is possible.

Let know what else you need to know...

Regards

Hydromech

 

[hydrometer]

Thanks, hydromech. I figured it would be best to put in a flow divider.

I was going to put it directly onto the main feed line which supplies both control valves(teed together).

I know it is a lot to ask but would this be the best option. I'm limited for room to install new equipment. The cavity they have all hoses and parts installed is very limited to space. You can't actually get to everything (typical) to even work on them. They company who built the machine doesn't even have a schematic of the system ; which doesn't help.

Anyway, any further advice would be appreciated

With thanks
Hydrometer

 

[hydromech]

Hydrometer...

Putting the flow divider on the tee before the control valves will work fine as long as you want the winches to run together. Unless both control valves are open the flow divider will not turn. The advantage of this method of installation is that the winches will be in sync in both directions.

In selecting the flow divider, you need to run it as fast as possible, it will be noisey but also more efficient...about 98%. Just find the maximum flow rate in litres per minute, muliply it by 1000 and divide it by the number of cc's/rev of all of the flow divider sections.

30 litres per minute = 30,000 cc's per minute
Flow divider has 2 sections at 6 cc's/rev total = 12
30,000/12 = 2500
Speed of flow divider = 2500 RPM...

Being as you used metric units, I guess that you are possibly in europe somewhere???

Slack & Parr in Kegworth UK make very very good flow dividers. Their website has all the details you will need.

The flow dividers have relief valves in them so you wont need to supply any.

That's about it...I think.

Just ask if you have more questions.

Regards

Hydromech

 

[hydrometer]

Hi Hydromech, sorry to take so long getting back to you.
I'm in Australia ( we also use metric).

What your saying is that if I put the divider BEFORE the tee, both winches will work together, does this include any pressure difference between the 2, what I mean is: if both are pulling a load each, and one requires a little more power, will they stay in sync or will one pull faster than the other. It's important that they pull at the same speed all the time ( or at least as close together as possible).

Also, with the divider in place, can I operate just one winch by itself?

 

[hydrometer]

Hi Hydromech, sorry to take so long getting back to you.
I'm in Australia ( we also use metric).

What your saying is that if I put the divider BEFORE the tee, both winches will work together, does this include any pressure difference between the 2, what I mean is: if both are pulling a load each, and one requires a little more power, will they stay in sync or will one pull faster than the other. It's important that they pull at the same speed all the time ( or at least as close together as possible).

Also, with the divider in place, can I operate just one winch by itself?


thanks again for your help

hydrometer

 

[kcj]

Q's:
-Is it a gear pump, or other fixed displacement pump? If so. you must have open center valves for each winch. The flow goes back to tank when winch valve is in neutral. Thus, a simple tee would not allow one winch at a time.
It would work if both winches were on together, but not one at a time. With load on one winch, all the flow just goes the other direction through the open center unused winch valve and to tank.

In that case, the 2 section gear flow divider, or 2 port spool dividor, would replace the tee.

Spool divider is cheaper, but I would go gear divider if the two winches must run independantly very much. Spool divider restricts flow to the unused side, which creates pressure drop, so half of the pump hp is going to heat.
If winch needs 2000 psi and 5 gpm, pump sees 10 gpm, 2000 psi, and wastes half to heat.

Gear divider actually transfers energy from the unused side over to the winch in use. If winch needs 2000 psi and 5 gpm, pump sees 10 gpm still, but only at 1000 psi. the energy is taken out of half the flow by the section acting as a motor, and driving tyhe other section as a pump. MUCH more efficient.

However, if this is intermittent, maybe max of a minute or two at a time, and you have sufficient tank volume, maybe the heat isn't an issue.

kcj

 

[hydromech]

Hydrometer...

The spool type of flow dividers theat kcj is referring to will work but they are not as efficient as rotary flow dividers. if you use one to drive two winches, you will always have one going slower leaving a slack rope, something you don,t want on a winch.

Rotary flow dividers are basically gear pumps that are tied together mechanically. It is this mechanical link that forces the gears to turn at the same speed. The oil displacement is therefor equal and so is the speed of the acutators.

A good rotary flow divider should be about 98%-99% efficient. With high running speeds and relatively equal loads on each winch, if one winch does 300 rev the other will do about 297. If one winch does 3000 revs the other will do 2970.

If you really want to know why there is a difference and how to compensate for it I will explain, but i dont want ot bore you with the details.

The flow divider cannot turn unless oil is allowed to flow through both sections The flow divider will work if one section is connected to a winch and the other is connected to tank. However, they are not designed to work that way, unequal loadings on the bearings will lead to a decreased life of the flow divider.

It's good to see questions from our antipodean friends!

Regards

Hydromech...

 

[hydrometer]

Hey guys, thanks very much for your help and explanations. It's good to see people are still willing to give advice and help others. I certainly appreciate it.

Geared divider seems to be the way to go I guess.

The controls are open centre (back to tank). So i gather one will still work if the other is stationary. If I could get a schmatic of the system I'd know a lot more. I think the 2 winch controls may have a power beyond feeding a second system ( a capstan head for each control), again , both capstan's can work together or seperate but they don't have to work in sync but if they do that's great.

Hopefully I'm on the right track

Again thanks

Hydrometer

 

[kcj]

One other thought: are you totally sure the winches operate at 50-50 flow? You will need a schematic to make sure.

Gear divider can be any ratio, but equal sections is most common. It can't be changed once built.

Spool dividers can be built to 50-50 or any ratio, or soem models are adjustable within a certain range, say 40-60 to 60-40. Might have to do that if the winch circuits are not exactly the same.

I'd still prefer gear dividers.

The power beyond should not effect it as long as they are open centers.

Also, look at the condition where one winch or capstand stalls, blocks flow. A spool divider will block off all flow to the other leg also, forcing all flow across relief at pump. A gear divider will either stall, or intensify so the pressure in the second leg is TWICE the pump relief valve setting. the barnes dividers I usemostly have sectional reliefs from outlet back to inlet to limit this intensification.

some of this may be beyond your interests, or not applicable, but you just need to be aware of the factors. As you are learning, even the simplest of real world circuits have many nuanaces and hidden glitches to watch out for. but you will get there, and learn a lot in the process. just always be aware of safety consequences, what woudl happen if anything in this circuit failed due to something we have not considered.

k

 

[HydroMET]

If using a gear type flow divider be careful of intensification.

hydroMET