Hydraulic system lines

SWilson3828 · Jul 18, 2023

Hello and thanks for advance for taking the time to read this post. Had some nice help from some posters on here when dealing with my 717 ZTrak hydraulic issues.
I know this is probably a pretty novice question but I'm going to ask because I'm a novice lol.
Does anyone know if the entire hydraulic system (high pressure lines, feeder and return lines pumps, motors) are an enclosed, pressurized system? The reason I ask is because I rebuilt the hydraulic pump that went out and it didn't produce any pressure. Figured the pump was beyond repair. Pushed the mower back onto the patio and there it sat for a couple days. I walked back out and there was a sizeable oil leak on the patio right under the rebuilt hydro pump. I looked and the leak was coming from the connection on the pump to the feeder hose. Wasn't a huge leak but it was definitely there. My question......is this line a pressurized line? If so then that may be the reason the pump isn't producing pressure. I know the high pressure hydraulic hoses to run from the pump to the motor and motor back to the pump are highly pressurized, but would the feeder and return likes from the fluid reservoir be pressurized as well? The entire feeder and return system for both the left and right pumps are combined and the left pump continues to work just fine. My guess is that if the entire system were pressurized and there was an air leak or poor connection then neither of the pumps would be working. Then again I don't know for sure. Thanks again for any info

x738 · Jul 18, 2023

The lines from reservoir to pumps and pump drains to reservoir appear to be held onto fittings with hose clamps, which would indicated that part of the system is not pressurized.

Lines between motors and pumps have pressure fittings.
These would be is is the high pressure circuits (depending or forward or reverse) that are not shown with the pumps /reservoir/filter section (above)

SWilson3828 · Jul 18, 2023

Yes they are held on by clamps. The original clamps were pressed clamps where you essentially had to twist and break them off but were replaced with the clamps you screw to tighten. Thank you for your reply.

Dave55 · Jul 18, 2023

I am going to say that a little different. You are probably looking at return lines and supply lines so there will be low pressure in them.
The supply lines might actually have negative pressure in them when the pumps are working.
Also if the leak is in the supply line from the tank to the pump, a leak may be letting air into the line when the pump is running, so it won't make pressure while air is in the line.
Those pumps are designed for pumping oil, not air.

x738 · Jul 18, 2023

Did you take any pictures of the pump when it was apart and what you repaired/replaced?

SWilson3828 · Jul 18, 2023

Dave55 said:
I am going to say that a little different. You are probably looking at return lines and supply lines so there will be low pressure in them.
The supply lines might actually have negative pressure in them when the pumps are working.
Also if the leak is in the supply line from the tank to the pump, a leak may be letting air into the line when the pump is running, so it won't make pressure while air is in the line.
Those pumps are designed for pumping oil, not air.

Yes I completely understand that. The thing is the leak is so small that I can't imaging it causing the suction side to not draw in adequate oil to build pressure. I'm thinking the "leak" is more the fastening clamp is not tight enough at the connection. Still....I'm going to replace all of the feeder and return lines and hope, by some miracle, that was the issue. Thanks for the reply

SWilson3828 · Jul 19, 2023

x738 said:
Did you take any pictures of the pump when it was apart and what you repaired/replaced?

HI. No I didn't take any pictures. I checked all of the parts and went over them with a fine tooth comb and the only grooves I found was on the valve plate, so I replaced that. The only thing I wasn't quite sure of was where the cylinder block makes contact with the valve plate. The surface of the piston cylinder where it touches the valve plate was completely flat. To me it didn't look like there was any wear on it but after the fact I looked at a new cylinder and there appeared to be some ever so slightly raised areas going around the edges of the top of the new cylinder block where as it appeared on mine they may have been worn off. I've attached an image of the new block where you can see the raised edges along the edge. Thanks for the reply

duckywi · Jul 19, 2023

I believe you are looking at case drains from the motors to tank. this need to be free flowing back to tank to prevent blowing out the motor seals.

Dave55 · Jul 19, 2023

Air molecules are smaller than oil molecules. If you have oil leaking out I will guarantee you have air leaking in when the pump is running. You can compress air, you can not compress oil. That is why hydraulics work like they do. You put pressure in the cylinder, it can't compress, so the piston moves away from the pressure. You want it to move the other way, change which side of the piston the pressure is on. That is also why you have to bleed air out of hydraulic systems, they do not work right if air is present.
Without knowing exactly what the leaking line is, it is impossible to guess if it is affecting your system. If the leak is a return line from motor to tank, it probably is not affecting the system. However if it is in the suction line going to the pump from the tank, it most likely is affecting your system by introducing air.

Off topic, but I found this very interesting

With the Oceangate Titan sub implosion I did a little research on how people went deeper that where the Titanic is. Answer was Trieste bathyscaphe.

https://en.wikipedia.org/wiki/Bathyscaphe_Trieste

People sat in the little ball hanging under the big flotation tank. The flotation tank was filled with gasoline. The gasoline was not used for anything other than flotation, gasoline is lighter than water. But gasoline being a fluid it is also not compressible, so the tank did not get crushed when it went to the bottom of the Marianna Trench to a point called Challenger Deep somewhere around 35,800 feet deep. that is almost three times as deep as where the Titanic wreckage is.
Also if you could chop Mount Everest (29,031 feet tall) off at sea level, turn it upside down and drop it in the Challenger Deep, the base of the mountain would be over a mile under water. Water pressure at Titanic wreckage is somewhere between 6000 and 6500 PSI. At Challenger Deep the pressure is about 15,750 PSI, so if you took a new oxygen tank full, dropped it into Challenger Deep, the tank would probably crush before it hit the bottom.
At Titanic depth the oxygen tank would not crush, but when you opened the valve water would go in with about the same force as oxygen comes out if you crank the valve open at sea level instead of oxygen coming out.

x738 · Jul 19, 2023

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SWilson3828 · Jul 19, 2023

duckywi said:
I believe you are looking at case drains from the motors to tank. this need to be free flowing back to tank to prevent blowing out the motor seals.

Thanks for the reply. Yeah I'm aware of the drains, but I'm talking about the little raised ridges

duckywi said:
I believe you are looking at case drains from the motors to tank. this need to be free flowing back to tank to prevent blowing out the motor seals.

Thanks for the reply. Yeah I know the drain channels in the top of the cylinder block, but I was more referring to the raised edges around the perimeter of the cylinder. There are 10 of those little ridges so I'm guess it's to provide a teeny amount of space for the oil to escape. The pistons in the cylinder all work smoothly

SWilson3828 · Jul 19, 2023

Dave55 said:
Air molecules are smaller than oil molecules. If you have oil leaking out I will guarantee you have air leaking in when the pump is running. You can compress air, you can not compress oil. That is why hydraulics work like they do. You put pressure in the cylinder, it can't compress, so the piston moves away from the pressure. You want it to move the other way, change which side of the piston the pressure is on. That is also why you have to bleed air out of hydraulic systems, they do not work right if air is present.
Without knowing exactly what the leaking line is, it is impossible to guess if it is affecting your system. If the leak is a return line from motor to tank, it probably is not affecting the system. However if it is in the suction line going to the pump from the tank, it most likely is affecting your system by introducing air.

Off topic, but I found this very interesting

With the Oceangate Titan sub implosion I did a little research on how people went deeper that where the Titanic is. Answer was Trieste bathyscaphe.

https://en.wikipedia.org/wiki/Bathyscaphe_Trieste

People sat in the little ball hanging under the big flotation tank. The flotation tank was filled with gasoline. The gasoline was not used for anything other than flotation, gasoline is lighter than water. But gasoline being a fluid it is also not compressible, so the tank did not get crushed when it went to the bottom of the Marianna Trench to a point called Challenger Deep somewhere around 35,800 feet deep. that is almost three times as deep as where the Titanic wreckage is.
Also if you could chop Mount Everest (29,031 feet tall) off at sea level, turn it upside down and drop it in the Challenger Deep, the base of the mountain would be over a mile under water. Water pressure at Titanic wreckage is somewhere between 6000 and 6500 PSI. At Challenger Deep the pressure is about 15,750 PSI, so if you took a new oxygen tank full, dropped it into Challenger Deep, the tank would probably crush before it hit the bottom.
At Titanic depth the oxygen tank would not crush, but when you opened the valve water would go in with about the same force as oxygen comes out if you crank the valve open at sea level instead of oxygen coming out.

Thanks for the reply. I do actually think the tiny leak is in the suction line running from the filter to the pump. It's either a tiny leak right at the connection or the connection isn't tight enough to make it air tight. I plan on changing those lines in hopes that that was the issue.

Hydraulic system lines

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