Hydraulic lift system Hydraulic, mechanical and electrical components of the lift system
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Old 06-23-2013, 04:26 PM   #1
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Default What is the Plastic Line For?

About 1 1/2 years ago I had to remove and repair the hydraulic cylinder. The piston rod was bent 1/2" and jammed. New rod, seals, wipers and parts and re-assembled without too much difficulty. While I was at it I temporarily reassembled the system on the A-frame to check it out before re-assembly under the trailer.

While doing this I noted the following features of the hydraulic system.

1. The pump discharge line to the cylinder is high pressure steel to handle high pressure. ( 1000 psi or so).

2. When you activate the lower switch, it opens the release valve on the pump and fluid returns to the reservoir via THE SAME STEEL LINE THAT FLUID WENT TO THE PUMP. In other words to raise the top, fluid goes to the cylinder, and to lower, the fluid return via the same line.

OK, so what is the purpose of the clear plastic tube at the end of the cylinder? It is low pressure, plastic, goes back to the reservoir, and has simple hose clamps and plastic fittings. IT IS NOT THE RETURN LINE. The fluid returns via the high pressure steel supply line.

I have asked numerous parties and many answer " it is the return line". No it is not. NoBody to ask at HiLo what they intended?

So I ask the forum, what the hell is this 1/2" clear plastic line for?

Naturally I have some ideas.

A. Vent Line: As the piston moves you have to vent air from the other side of the piston so no pressure build-up in the cylinder.

B. Leakage: If there is any leakage ( weepage, seepage, what-ever) around the piston,the plastic line will route it back to the cylinder. Otherwise ATF fluid could. build up on the wrong side of the piston.

C. Standard Piston: The HiLo cylinder is one-way. Pressure on only one side of the piston. Some services are two-way with fluid on both sides. The supplier may make a standard cylinder with openings on each end. ( you just plug the end you don't use).

D. My plastic line always has a little red fluid in it. Does anyone have a clear line with no evidence of red ATF fluid being in it?

OK, so I throw it open. What is the clear plastic line for? It is not a return line.
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Old 06-23-2013, 04:34 PM   #2
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I vote for B. Leakage: If there is any leakage ( weepage, seepage, what-ever) around the piston,the plastic line will route it back to the cylinder. Otherwise ATF fluid could. build up on the wrong side of the piston.
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Old 07-04-2013, 11:38 AM   #3
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Default Plastic Line

OK, this one did not generate too much interest. So here is the summary as I see it.

1. When the top raises, high pressure fluid flows from the pump thru the steel line to the cylinder, extending it.

2. When you hit the lower switch, it opens a valve at the pump and fluid returns to the reservoir via the same steel line. The weight of the top forces the fluid return.

3. The clear plastic line is a vent for the other side of the cylinder. In an ideal world there would be little or no leakage and the plastic line would be clear. In the real world there will be seepage, leakage, etc and some red fluid will appear in the plastic line. Large amounts of fluid in the plastic line can be a pre-cursor to cylinder trouble.

4. My official Hi-Lo manual says " inspect the cylinder and if EXCESSIVE leakage occurs seek service". There you have it.

4
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Old 07-04-2013, 12:13 PM   #4
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Default I don't know

I've only been under mine once and tried to give it an eyeball. Found and followed the propane line (stove, fridge, heater), the two hydraulic lines that you mention, and an unidentified (NOT WATER) plastic tube - similar to the return hydraulic line.

I haven't a clue where it originates nor terminates. At the time I didn't care, but you've reminded me of it. As I recall it came from the front-side and didn't extend but halfway, towards entry side, maybe towards heater? Any ideas?

I guess if it ever stops raining (and the ground dries up) I'll investigate.
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Old 07-05-2013, 09:43 AM   #5
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Default What is under trailer?

On mine there are the following lines

1. Steel hydraulic line, from pump to hyd. cyl.2. Plastic cylinder vent line, from hyd cyl back to pump
3. Propane gas line to appliances, furnace, stove, refrig.
4. Plastic line which protects wiring from front to master switch, this goes from battery location back to master switch location.
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Old 07-05-2013, 10:18 AM   #6
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Quote:
Originally Posted by edward lansing View Post
OK, so what is the purpose of the clear plastic tube at the end of the cylinder? It is low pressure, plastic, goes back to the reservoir, and has simple hose clamps and plastic fittings. IT IS NOT THE RETURN LINE. The fluid returns via the high pressure steel supply line.

I have asked numerous parties and many answer " it is the return line". No it is not. NoBody to ask at HiLo what they intended?

So I ask the forum, what the hell is this 1/2" clear plastic line for?

Naturally I have some ideas.

A. Vent Line: As the piston moves you have to vent air from the other side of the piston so no pressure build-up in the cylinder.

B. Leakage: If there is any leakage ( weepage, seepage, what-ever) around the piston,the plastic line will route it back to the cylinder. Otherwise ATF fluid could. build up on the wrong side of the piston.
You are correct.

The Hi-Lo cylinder is a single action type. This means that hydraulic pressure is applied to one side of the piston to extend it. To retract it, the pressure is bled off and the hydraulic fluid returns to the reservoir via the same high pressure line.

Single acting cylinders need to be able to vent the air on the side of the piston opposite the pressure. Otherwise, the air will compress and the piston will stop moving. The vent on the Hi-Lo cylinder is attached to a hose that returns to the reservoir. There is always a bit of fluid leakage between the piston rings and the cylinder. This fluid is also vented out the hose. So, it is normal to see a bit of fluid in the hose. Moreover, a lot of fluid in this line may be an early indication that the piston rings are not sealing well.

The top cylinder in this picture is a single acting type: http://www.blogs.caltav.com/wp-conte...jhsgdfgvar.jpg
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Old 07-05-2013, 10:37 AM   #7
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Default Thanks for this Mr EL

4. Plastic line which protects wiring from front to master switch, this goes from battery location back to master switch location.

That's likely what I viewed then. Now, why is it located underneath the camper rather than inside?
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Old 07-05-2013, 02:43 PM   #8
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Default Plastic Line Routing

Probably ease of construction and save $. Otherwise you would route out of battery box, into trailer, thru furnace compartment, behind dinette, and into compartment where master switch is located. Easier to route under trailer and up to master switch.
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Old 07-05-2013, 02:56 PM   #9
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Default Norton Rider Cylinder Picture.

Great picture. So that is where the piston seals and wipers are!

I note that my Hi-Lo manual says " inspect cylinder and fix IF EXCESSIVE LEAKAGE". I guess this would be a plastic line full of red fluid.

I would raise the top about half way and STOP. If it stayed in position there would probably be no or minimum leakage past the piston seals indicating degraded performance.

If the top moved, this would indicate leakage around piston seal and the need for removal and repair.

If so see the extensive posts on removing and repair.

This is where I came in so GOOD LUCK to all.
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Old 07-05-2013, 03:41 PM   #10
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Default EL

re-reading this forum again, and now with hind-site, I remember that my clear hydr. return line was in fact still clear with no hint of fluid or discoloration/ the top was up at the time.

At least that's what I observed, and I'm sticking to it.
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