Relocating Air/Hydraulic Pump Question

[Kevin Means]

We are relocating some components to make room for our subframe and habitat. Two of those components are the hydraulic manifold and the air/hydraulic pump. (We're thinking about replacing the pump with a 12 volt pump, but the OEM pump we have was recently rebuilt and works well.) The manifold will be about two feet higher than it's normal position and will be mounted on the black bracket shown in the picture. We are planning to mount the pump in the location shown in the other picture, but it will be about 3" higher than what is shown in the picture.

When the two components are relocated to their new positions, they will be pretty much level with each other. In their factory installed positions, the pump is much higher than the manifold I know it's a sealed system, but I'm no hydraulics expert, so I was wondering if there is any problem with the relative heights of those hydraulic components being level vs. one higher than the other. Thanks

Kevin

 

[Ronmar]

no problem that i can see. in the end fluid does not flow unless cylinders are moving and vis-versa...

The problem with electrics is finding one small enough to properly feed this tiny system. most all you will find are grossly oversized. since this system is flow restricted and has flow related safeties, it can only accept so much flow(1/3-1/2GPM MAX). Electrics know one thing: Make rated flow? they will do this regardless of whether the system can accept it or not. if the system can accept more, the electric HPU will build whatever pressure is needed to move the load and then flow at full rated flow.

If the system cannot accept the flow the Electric HPU will still flow its rated amount by running to maximum pressure, opening and flowing most of the fluid thru the safety relief. Because of this the pump, wiring and battery will always run at max load requiring larger wires and battery capacity than the work really needs.

Closest i came to being appropriately sized was a marine hydraulic trim pump, used to tilt and lift outboard motors and actuate trim tabs...

 

[Kevin Means]

Good to hear. Ronmar, I was wondering why I hadn't seen many electric conversions. Now I understand why. Nothing wrong with my OEM system - I just kinda wanted a more steady flow than the "clunk, clunk, clunk" of an air/hydraulic pump. For now, I'll just stick with it. Thanks

Kevin

 

[B-Dog]

I'd ditch the whole system and do a manual pump - Ronmar has some good info posted. You're not using the suspension cylinders or the spare tire anymore so it's a lot of existing system/plumbing for the cab tilt. Unless you think you're going to be breaking down on the daily, the manual pump is not difficult to manage.

 

[Keith Knight]

Not a bad idea.

 

[Ronmar]

Yea the hand pump works great, and is dead easy… i have done 3 videos on the one I chose… here is the first one…

 

[Kevin Means]

I have seriously considered doing just that B-Dog, especially after watching Ronmar's videos about his manual pump (only) setup. I've watched that video and the follow-up video about his flow-control solution. However, I like the idea of redundancy, even at the cost of simplicity, so my preference is to keep either the OEM air/hydraulic pump, or (ideally) replace it with an electric pump. After reading Ronmar's post about most electric pumps being too powerful, It's clear that the OEM pump is the simplest solution for our needs. (Ours is freshly rebuilt) If someone has a viable electric pump in mind, I'd love to hear from you.

Kevin

 

[Kevin Means]

Interestingly, I came across a video of a converted LMTV (Acela) which shows their cab tilting with an electric hydraulic system.

If you skip forward to the 6:45 mark, you can see how fast it raises the cab. Compared to my freshly rebuilt air/hydraulic system, it rockets up when it tilts. I did a bit of online research but couldn't determine what pump they're using.

 

[Ronmar]

Interestingly, I came across a video of a converted LMTV (Acela) which shows their cab tilting with an electric hydraulic system.

If you skip forward to the 6:45 mark, you can see how fast it raises the cab. Compared to my freshly rebuilt air/hydraulic system, it rockets up when it tilts. I did a bit of online research but couldn't determine what pump they're using.

And I suspect they will not tell you that info... They like to keep their info to themselves, and unless a customer tells you about it... My hand pump is faster than the AOP

 

[GeneralDisorder]

Acela deletes the check valves in the rams leaving the system un-metered in the case of a hose failure. Let me say that another way - DAVE (Acela's owner) doesn't give a fast flying fart if one of his trucks crushes someone's skull between the tire and the step. And no that's not fanciful thinking - multiple soldiers have been killed by FMTV cabs. Including a poor guy who's skull was crushed by the step and the tire.

 

[GeneralDisorder]

And this is the flavor of 24v unit used by the military for the A1P2 armored cab. It can be ordered down to 0.14 GPM:

https://ph.parker.com/us/en/product-list/compact-hydraulic-power-unit-108-series

Acela uses something similar, but specifically wanted it faster, and Quade Sheehan clued them in on deleting the cylinder flow control check valves when they complained that their pumps were causing some of the rams to lock out. I'm guessing all of them know, deep down. they deleted a safety feature and just don't care - figuring it will never get back to them because should it happen, no one will ever figure out why the guy died - they will just figure it was a freak accident. Or blame it on old Army surplus, the E4 mafia, or the alignment of the stars or just won't answer their phone.

 

[B-Dog]

Good gracious! Those are some bold accusations, I would hope they're speculative!

I don't know what Acela does but there are safe alternatives to get faster motion without the liability risk of losing everything.
A quicker up travel could be accomplished by simply raising the pump pressure.
You could set up some check valves parallel with normally closed valves with orifices, which would offer free flow up and regulated flow down, redundant, all packaged into a single manifold.
Air in the system is probably the biggest but that's true for the stock system all the same.

 

[GeneralDisorder]

It is not speculation. I have worked on multiple of their trucks, seen it in person, and got the information from the horses mouths so to speak. They drill out the check valve set screws and weld up the hole. All you have to do is look at their rams to see the weld on the side.

 

[Ronmar]

Increasing pressure will only increase speed if flow also increases. IE: it is the volume flowing into the cylinder that determines how fast the piston/rod moves. Pressure determines the force generated by the piston pushing the rod(PSI X piston area = rod force)

the safety checks don’t really care about pressure. It is the friction of the flow past the check ball that pulls them against a spring. with enough flow ultimately compressing the spring enough to push the ball into a valve seat and block the flow/lock the cylinder.

the OEM system has restricted orifices in the control valve that limits flow below a point where the safeties will activate. Thats why most readily available electrics are gross overkillthey still make their rated flow but only a tiny part of it flows thru the restrictions with most passing thru the relief valve.

it is like driving a finish nail with a sledge hammer with a tiny amount of energy doing the work and the rest making oil, motor and wire heat while heavily loading the battery.

any pump system should have the safety relief reset to just over what is required to actually lift the cab(1.5-2K?).

you can do as you suggested, remove the safeties and restrictors and place a flow control like I used on my manual at the cylinder base for unrestricted flow up, and metered flow down. A blown hose in this scenario would still allow the cab to come down but at its normal speed with little ability to quickly stop it(access and close needle valve at cylinder base).