Question about Hydraulic Fluid Dynamics

[backagain]

If I change a 1/8" ID hose to a 1/4" ID hose, I know that increases flow but how does it change pressure?

I'm changing the hydraulic lines from a synchronization valve to two rams of a slide-out. The lines from the pump to the sync valve are 1/4" ID. The lines from the sync valve to the rams are 1/8" ID. This is a small slide-out and operates fairly quick. I'm concerned the larger ID lines will make the slide-out rams operate TOO quick. What do you think?

Doug '05 Country Coach Affinity

[Mr_D]

Static pressure or dynamic pressure? Volume will be more if the pump can supply it. Static pressure will be the same. Dynamic pressure will be less since the flow is higher.

[KanzKran]

Originally Posted by backagain

If I change a 1/8" ID hose to a 1/4" ID hose, I know that increases flow but how does it change pressure?

It won’t change the flow, and there will be a small reduction in pressure drop along the length of the hoses since fluid speed will be reduced for the same volume rate of flow. The pump is a positive displacement type, meaning for every revolution it will move a set amount of fluid regardless of pressure.* So the actuators will still move at the same speed, and they’ll still produce the same force.

*There actually will be a small reduction in flow rate with increased pressure, know as pump volumetric efficiency (some oil sneaks past the gears or pistons), but that’s not relevant here. Centrifugal pumps, on the other hand, will change flow greatly with changes in pressure, and curves have to be used. Like fans.

[Doughydman]

I would stay with same size as oem provided. Could potentially operate much faster. Can’t think of a good reason to upsize hose if it’s already moving plenty fast. Hoses were sized that way for a reason.

[backagain]

Wow, you guys are great!! It sounds like KanzKran and Mr_D are saying about the same thing, so my plans should not be an issue with the slide-out function.

[backagain]

Originally Posted by Doughydman

I would stay with same size as oem provided. Could potentially operate much faster. Can’t think of a good reason to upsize hose if it’s already moving plenty fast. Hoses were sized that way for a reason.

I'm replacing due to a leak. They want 4x the price for oem, maybe because the oem size hose is almost impossible to find. 90% of the answers from other forums say there will be no difference including a mechanic who formerly built Country Coaches. I agree that staying with oem is usually the best idea, but not always.

[KanzKran]

Originally Posted by backagain

Wow, you guys are great!! It sounds like KanzKran and Mr_D are saying about the same thing, so my plans should not be an issue with the slide-out function.

Pretty much. He did bring up a point I neglected, since my work involves constant-speed pumps almost exclusively (diesel and induction motor driven): with reduced pressure loss in the lines due to friction, the pump may actually run a little faster since it's driven by a DC motor, which will have a large speed range depending on torque load. But without knowledge of a large pile of parameters, how much of an affect that is would be just speculation, though for most systems, flow losses are a relatively small portion of the total pressure at the pump when loaded to rated pressure, assuming a simple system.

[backagain]

Originally Posted by KanzKran

with reduced pressure loss in the lines due to friction, the pump may actually run a little faster since it's driven by a DC motor

Just as long as slide-out doesn't turn into a catapult

[RiverBurt]

Originally Posted by backagain

Just as long as slide-out doesn't turn into a catapult

Thanks for that visual!

[lwmcguire]

Originally Posted by Mr_D

Static pressure or dynamic pressure? Volume will be more if the pump can supply it. Static pressure will be the same. Dynamic pressure will be less since the flow is higher.

Exactly as Mr_D stated and you can use a restrictor or orifice however I think you could get your fingers off the switch in time

You want it sealed properly in or out

[twinboat]

You can buy fittings, thread and plug them internally, then drill out the plugs as restricters.

Even a inline valve that you partially close will work.

I needed to do that on an old ( 50s ) truck mounted snow blower. The new trucks hyd system would move the discharge shoots to fast, bending things.

[Lee650]

Assuming you will refill the system with hydraulic oil, you will notice no difference in function, nor will the system if you replace the lines with quarter versus eighth inch lines and no other added components. It's the equivalent of replacing tiny wire with the next size larger; less friction loss in the lines.
Your saying the OEM lines are hard to find and more expensive makes me wonder why the OEM used them in the first place, but I have that question frequently regarding RV's in general.

[lwmcguire]

Originally Posted by Lee650

Assuming you will refill the system with hydraulic oil, you will notice no difference in function, nor will the system if you replace the lines with quarter versus eighth inch lines and no other added components. It's the equivalent of replacing tiny wire with the next size larger; less friction loss in the lines.
Your saying the OEM lines are hard to find and more expensive makes me wonder why the OEM used them in the first place, but I have that question frequently regarding RV's in general.

You will get increased gpm therefore the op question

Increased flow moves the slide faster given nothing else changes

[twinboat]

Changing lines from 1/8 to 1/4 of an inch doesn't souund like much but you are doubling the diameter. That's 4 times the area and a whole lot less friction loss.