Technical question about hyd cyl.

   / Technical question about hyd cyl.
  • Thread Starter
#11  
Could air possible leak by the rod seal.

Those seals are designed to keep fluid in, with the lip facing inward.
 
   / Technical question about hyd cyl. #12  
Even if "air were sucked in" , or a "Vacuum were formed".

The MAXIMUM contribution to the load would be 14.7 pounds per square inch.

Compared to "typical" hydraulic pressures, that's not much change. About the amount that might be termed "friction losses.

Even a 2 inch piston area with a 2000# load is looking at 1000 psi. What's plus or minus 15psi gonna do?

This entire thought exercise is about leakage!

Note, Due to the parking situation in the lower barn. The Hurlimann is parked with the FEL UP (Horror!)
That bucket doesn't fall two inches in two weeks. Seems like a tight system of valves and cylinder packings to me. Oh! Nothing in the bucket ;-)
 
   / Technical question about hyd cyl. #13  
Could air possible leak by the rod seal.

Those seals are designed to keep fluid in, with the lip facing inward.

JJ

It's not if air would leak in, FLUID (Which is relatively non compressible) would need to leak OUT!
 
   / Technical question about hyd cyl. #14  
Could air possible leak by the rod seal.

Those seals are designed to keep fluid in, with the lip facing inward.

I still cant see how 14.7 psi air is going to leak in when the fluid behind the seal is anywhere from 500 to 2000 PSI depending on the cylinder size which you did not specify. But in any case the rod end will have pressurized fluid in it. I can see fluid leaking out, causing the rod to move downward eventually over time, but I sure can't see air leaking in. If the rod seal never leaks anything then the rod and its load will never move.
 
   / Technical question about hyd cyl.
  • Thread Starter
#15  
Let me put it another way.

If the rod end is extended and up, and a load is pushing down on the rod, and the cyl is closed off, could air get by the rod seal.

Excerpt:

Air can enter the system through a cylinder rod seal.
Vacuums in excess of 20 inches of
mercury have been recorded in systems
without anti-cavitation check valves. This is
enough to force dirt particles past the shaft
seal into the system with the air.

When you raise a full bucket in the air, and it is down on the ground within hours or overnight, and if the cyl is sealed off by a good loader valve, what would you say is the cause of the bucket descent?

If you say piston seals, that means that the fluid transferred from one side of the piston to the other side.

Sometimes, I don't always understand what I read or hear, so even at 74 yrs I am still trying.
 
   / Technical question about hyd cyl. #16  
Let me put it another way.

If the rod end is extended and up, and a load is pushing down on the rod, and the cyl is closed off, could air get by the rod seal?


In this case yes, it might be possible.
 
   / Technical question about hyd cyl. #17  
Let me put it another way.

If the rod end is extended and up, and a load is pushing down on the rod, and the cyl is closed off, could air get by the rod seal.

Excerpt:

Air can enter the system through a cylinder rod seal.
Vacuums in excess of 20 inches of
mercury have been recorded in systems
without anti-cavitation check valves. This is
enough to force dirt particles past the shaft
seal into the system with the air.

When you raise a full bucket in the air, and it is down on the ground within hours or overnight, and if the cyl is sealed off by a good loader valve, what would you say is the cause of the bucket descent?

If you say piston seals, that means that the fluid transferred from one side of the piston to the other side.

Sometimes, I don't always understand what I read or hear, so even at 74 yrs I am still trying.

Just for perspective......

Run this mental example through your mind once again

This time, use a single acting cylinder..


Take the example to any extreme would would like ........ Use water for the working fluid, it will boil if you get the "Vacuum" high enough. (pressure low enough)

But in the end, It's only fluid leaking past "seals" and closed ports that allows the piston to move relative to the cylinder.
 
   / Technical question about hyd cyl.
  • Thread Starter
#18  
Of course it is fluid leaking past the seals, I thought I said that.

Now, a good SA valve is in the neutral position, can a SA cyl suck in air if a load is placed on an extended cyl.
 
   / Technical question about hyd cyl. #20  
Of course it is fluid leaking past the seals, I thought I said that.

Now, a good SA valve is in the neutral position, can a SA cyl suck in air if a load is placed on an extended cyl.

Where would the displacement of volume come from ? The cylinder is full of oil, and the valve is "good".

If no fluid goes out, there is no place for air (a different fluid) to enter.

Logic...not magic.
 

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