Running a Single Acting cylinder on a double acting valve.

[Roger66]

I have added a 3 stage forklift rack to my tractor for high lifting. It works super good, but I'm running this single acting forklift rack off of a double acting valve meaning that while i'm lowering the forks the valve is deadheaded which can build heat and is not ideal. I'm using a Prince Stack valve so I could easily just add a single acting valve to the stack to solve this. Adding the additional section is a easy and cheap solution, but I'm wondering if I can do better. I'm not lifting heavy weights, so the forks take forever to lower. I was wondering since I have a double acting valve anyway, could I use a Venturi vacuum effect to suck the fluid out of the cylinder to increase the lowering speed of this single acting cylinder? What do you think, any legs to this idea? The concept works with air which is a "fluid".

 

[Rich B1]

If it were mine, I would add the single acting valve and be done with it. You don’t want a lowering circuit to run too fast due to safety and risk of cavitation

 

[MTGreen]

That's an interesting concept, but I'm trying to understand how that could be put into practice with a double acting valve. You currently have a single acting ram which uses one port for input and output. Your double acting valve which presumably is an open SCV type has 2 cylinder ports. When you pull the lever one way you get pressure down one of those ports and the other port opens to reservoir. Pulling the valve the other way will give flow out the unused port in your SCV, but what I'm unclear on is how you could use this flow necked down to create a vacuum plumbed in to your single hose for your single acting cylinder WITHOUT providing a bypass to reservoir when you want to extend your cylinder. I suppose it's possible using solenoid valves or a complicated arrangement of pilot operated valves - or am I missing something here?

It would seem to me that adding the single acting valve to the stack, trying to identify and address any restrictions in the plumbing, swapping to a double acting cylinder, or reducing cylinder diameter would be simpler solutions

 

[ptsg]

That's more or less how I run mine. Even though I'm using a double acting cylinder on my dump trailer, I'm using it as single acting with a breather on the non used port of the cylinder. In my case, since I have an hydraulic winch, I run the winch in free spool as I lower the dump trailer. Works great and I'm not forcing fluid through the relief valve at max pressure.

You can either add a single acting valve, probably the best move if you don't mind the cost too much. Or run a hose straight to the tank on the not used port on the current double acting valve, probably quite a bit less costly too.

 

[Roger66]

The cylinder size is massive and the hoses are only 3/8". I can't imagine it's possible to make it so fast it's even close to a safety concern. I hadn't thought of cavitation. What is the risk there? Keep in mind this is a home use piece of equipment and it's not used often. It just would be nice if I could lower it a little quicker. It seems to take forever if forks are lightly loaded and it's cold.

 

[MtnViewRanch]

Get a valve with the float feature.
Use the float feature to lower the mast.
This way you still have the use of the valve for other applications.

 

[Roger66]

Just so you can see what this contraption looks like.

 

[oldnslo]

The cylinder size is massive and the hoses are only 3/8". I can't imagine it's possible to make it so fast it's even close to a safety concern. I hadn't thought of cavitation. What is the risk there? Keep in mind this is a home use piece of equipment and it's not used often. It just would be nice if I could lower it a little quicker. It seems to take forever if forks are lightly loaded and it's cold.

I would run larger hose since that would help increase flow at low pressure when gravity lowering. You probably only have around 200 PSI load induced pressure with empty forks.

 

[Roger66]

Get a valve with the float feature.
Use the float feature to lower the mast.
This way you still have the use of the valve for other applications.

The float type valve is a great idea for single/double acting on the same SCV. I still which I could pull this down faster. It probably takes 2 minutes to lower this.

 

[Roger66]

I would run larger hose since that would help increase flow at low pressure when gravity lowering. You probably only have around 200 PSI load induced pressure with empty forks.

Larger hoses might help some, but it was still quite slow even in it's stock configuration on the forklift I robbed this off of. I used that old Clark electric forklift for 10 years or more until it finally broke enough to scrap it. I suspect some of the problem is age. There are many gears, chains and rollers that probably don't roll as well as new. A tiny bit of friction here and there all adding up along with the undersized hoses & SCV valve.

 

[MTGreen]

Just so you can see what this contraption looks like.

View attachment 774024

Looks useful. Stability looks to be a concern

 

[Farmer495]

Double acting valve with float feature handles single acting cylinder easy, I have a wagon hoist, just put lever in float and it drops on it's own. I have used in on a double auto cancel valve and the only way to lower it with out deadheading/loading the used port was to just lightly hold the lever in "lower", locking it in caused loading.

 

[CobyRupert]

Is running a single acting cylinder on a double acting valve really a concern?
My experience with single acting cylinders is limited and it’s been awhile, but I don’t remember paying any attention to the specifics of the SCV I plugged them into.
I’m thinking of a mower. Does pump dead-head and go into relief for a second or two when you lower it each time? And what are the harmful results?

 

[Farmer495]

Is running a single acting cylinder on a double acting valve really a concern?
My experience with single acting cylinders is limited and it’s been awhile, but I don’t remember paying any attention to the specifics of the SCV I plugged them into.
I’m thinking of a mower. Does pump dead-head and go into relief for a second or two when you lower it each time? And what are the harmful results?

Not sure on how much real harm is done for a few seconds on relief, I did find that light touch on lever just allows the oil to flow "out" and not get pressurized the opposite other way.

 

[MF243RedTop]

Just so you can see what this contraption looks like.

View attachment 774024

Need to have the heaviest attachment you have on the 3pt hitch when operating with the lift on.

Great ingenuity!!

 

[kennyd]

Have you checked your reservoir when that thing is up that high? That cylinder has a lot of fluid in it!

 

[Roger66]

Perhaps dead heading was the incorrect term. The valve is going into relief, but it's not for a second or 2, it's a minute or 2 to lower this. I don't think this is really harmful, it will heat the fluid, but I don't use this hard or often.

Stability is certainly a concern and I'm really careful and aware of that. The tractor however is longer, wider and probably just as heavy as the forklift it was previously. I use a ballast box filled with steel plates and lead. The Ballast box weighs somewhere over 2,000 lbs. The Forklift of course had solid tires and was intended for use on concrete floors in a warehouse. I still think this tractor setup is safer than how I was using my old forklift.

The reservoir volume is a real concern. I have no way to verify that. My dipstick only reads full or not. it's only about 1" in the fluid.

The real question is could I use the blocked flow from the valve to create a venturi effect like a jet pump to increase the downward speed of this by sucking the fluid out of the single acting cylinder. Something like the image below. Imagine the currently blocked flow is the air gun, the jar is the single acting cylinder and the spray is the return line to the tank.

 

[oldnslo]

A Venturi might help but will it aerate the oil to the point that you start cavitating the pump.

 

[npalen]

Is there an orifice hidden in the plumbing to the cylinder that is causing it to be slow on the downstroke?

 

[MTGreen]

Perhaps dead heading was the incorrect term. The valve is going into relief, but it's not for a second or 2, it's a minute or 2 to lower this. I don't think this is really harmful, it will heat the fluid, but I don't use this hard or often.

Stability is certainly a concern and I'm really careful and aware of that. The tractor however is longer, wider and probably just as heavy as the forklift it was previously. I use a ballast box filled with steel plates and lead. The Ballast box weighs somewhere over 2,000 lbs. The Forklift of course had solid tires and was intended for use on concrete floors in a warehouse. I still think this tractor setup is safer than how I was using my old forklift.

The reservoir volume is a real concern. I have no way to verify that. My dipstick only reads full or not. it's only about 1" in the fluid.

The real question is could I use the blocked flow from the valve to create a venturi effect like a jet pump to increase the downward speed of this by sucking the fluid out of the single acting cylinder. Something like the image below. Imagine the currently blocked flow is the air gun, the jar is the single acting cylinder and the spray is the return line to the tank.

View attachment 774156

I don't know that that picture is illustrating the Venturi effect. The flowing air does create a vacuum in the copper tube; but my understanding is that to be called a Venturi effect the creation of a low pressure/suction must be accomplished by necking down or creating a restriction in a flowing fluid similar to how a carburetor pulls fuel in. I think the picture is more like the old crankcase vents which were just hoses run underneath the vehicle. The passing air at a right angle to the hose created a suction in the hose and the oil just dripped out onto the asphalt as the vehicle was going down the road.