What's the purpose of a bypass on a cylinder?

[avz]

I've seen on some cylinders that there is a sort of a bypass tube (I guess that it's not the correct terminology) installed (welded) on them. could you please tell me what's the purpose of it? thanx.

 

[TractorTech]

What kind of equipment are you talking about? Engine? Diesel? Welded where?

 

[jaxs]

Bypass is used to (A) limit applied pressure (B) prevent pump deadheading at more than design pressure (C) prevent hose/line/pipe rupture due to over-pressurizing (D) prevent personal injury from high pressure explosion. (E) recirculate fluids to keep 2 or more solvents mixed and in suspension (F) recirculate fluids through cooler and/or filter.
Not an all inclusive list but enough to convince you bypass is a neccessary feature.

 

[Rich B1]

Some cylinders have both ports located near each other to simplify hose routing. The tube is used to supply oil to the other end of the cylinder.

You will also see tubes welded on when the cylinder has a block on it for a holding valve.

 

[jb1390]

I've seen on some cylinders that there is a sort of a bypass tube (I guess that it's not the correct terminology) installed (welded) on them. could you please tell me what's the purpose of it? thanx.

You are probably seeing the line to pressurize the upper part of the cylinder. Lots of cylinders run that in hard line attached to the cylinder itself. Makes it so the flex hoses only need to be routed to the base of the cylinder.

 

[avz]

Bypass is used to (A) limit applied pressure (B) prevent pump deadheading at more than design pressure (C) prevent hose/line/pipe rupture due to over-pressurizing (D) prevent personal injury from high pressure explosion. (E) recirculate fluids to keep 2 or more solvents mixed and in suspension (F) recirculate fluids through cooler and/or filter.
Not an all inclusive list but enough to convince you bypass is a neccessary feature.

Thanx for the comprehensive reply but I would like to understand how it works since as I understand, that bypass supplies the oil simultaneously to both sides (upper and lower) of the piston, which to my limited understanding, would've prevent it from moving, and yet, it works. what am I missing?

 

[jb1390]

Thanx for the comprehensive reply but I would like to understand how it works since as I understand, that bypass supplies the oil simultaneously to both sides (upper and lower) of the piston, which to my limited understanding, would've prevent it from moving, and yet, it works. what am I missing?

Read my first reply. I don't think what you are looking at is a bypass line. Typically a relief valve is included within the control valve. Not the cylinder.

For clarity, I'm assuming you are talking about a line like this one pictured?

 

[WranglerX]

Think you are looking at a steel tube that supplies hydraulic pressure to one side of cylinder/piston .... Mainly it bring both connection "ports" to same location so you don't need longer hose to go the side of piston further from the valve...

 

[flyerdan]

The welded line is a feed to one of the ports, both to keep hose length shorter and keep from having a vulnerable hose exposed more than necessary. The double acting valve will feed pressure to one side only and allow the other side to flow to the return line.
There will be a bypass in the system, but it will be at the front of the valve body to prevent stuff from getting tore up from overpressure.

 

[LouNY]

There is a situation were cylinders may have a "bypass" it is when Rephasing cylinders are used in a multi cylinder application.

Rephasing Hydraulic Cylinder Solutions

Of course there are also pilot operated hydraulic check valves which will have some extra pipeing on them, they are handy devises at times and a pain in the butt other times.
They require that a cylinder is actively powered to operate they lock the fluid in a cylinder untill pressure is applied to move the cylinder they are the safety valves often used on manlifts and such equipment.
They are also found on more expensive hydraulic toplink cylinders.