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Air vs hydraulic cylinders???
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Topic: Air vs hydraulic cylinders??? (Read 12844 times)
bevans6
Hero Member
Posts: 6205
1980 MCI MC-5C
Air vs hydraulic cylinders???
«
on:
March 22, 2013, 06:14:34 AM »
I had a question about the difference between air cylinders vs hydraulic cylinders. Hydraulic cylinders are easy to find, cheap as chips, many different sizes and configurations, rated to 3,000 psi usually. Air cylinders are a lot harder to find, a lot more expensive, and I only need 150 psi for the bus maximum. Is it possible to take a hydraulic cylinder and use it with air pressure? What are the key internal differences to think about? I am thinking of two applications off the top of my head - MCI style clutch assist, which is single acting, and door open/close which is double acting.
Thanks, Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Allison MT-647
Tatamagouche, Nova Scotia
bansil
Full Member
Posts: 201
Re: Air vs hydraulic cylinders???
«
Reply #1 on:
March 22, 2013, 08:56:05 AM »
how much stroke do you need for the door?
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Doug
Mnt City TN
Member of:
PP
Will & Wife
Hero Member
Posts: 1521
Re: Air vs hydraulic cylinders???
«
Reply #2 on:
March 22, 2013, 09:20:37 AM »
Air volume moves much faster than hydraulic oil and the seals on a hydraulic cylinder are fabricated with oil in mind. If you run them dry, they won't last long. I know that first hand from working on heavy equipment. Of course, that was many years ago and seal technology has probably changed.
Will
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Fulltimers
Prevost 892 Silver 754
http://www.amazon.com/Will-Decker/e/B003CVL1ZM/ref=sr_tc_2_0?qid=1415040796&sr=1-2-ent
OneLapper
Hero Member
Posts: 861
Re: Air vs hydraulic cylinders???
«
Reply #3 on:
March 22, 2013, 10:45:58 AM »
Brian,
I'm looking into the clutch assist thing too. I think air is going to be the way to go. I thought about using the power steering pump for the hydraulic assist cylinder on the clutch. The air assist is probably cheaper in the long run since you don't need expensive hydraulic hoses, control valves, and return to sump setup. Fluid flow regulators are more expensive. I would also think that fluid viscosity (cold to hot) would affect the assist quite a bit. The air assist would be more consistent.
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OneLapper
1964 PD4106-2853
www.markdavia.com
luvrbus
Hero Member
Posts: 26049
Re: Air vs hydraulic cylinders???
«
Reply #4 on:
March 22, 2013, 12:43:46 PM »
Why not just go to a truck wrecking yard and buy the master cylinder and slave cylinder off a truck or buy the setup off a wrecked Prevost they have used it for years then you don't have all the design time and a proven unit
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Life is short drink the good wine first
bevans6
Hero Member
Posts: 6205
1980 MCI MC-5C
Re: Air vs hydraulic cylinders???
«
Reply #5 on:
March 22, 2013, 12:55:27 PM »
To be clear, I am asking if I can substitute a hydraulic cylinder that would normally use oil in an application that would use air. I can get a 2" bore 8" stroke hydraulic cylinder with the fittings I need down the street for almost free (just as an example), while an air cylinder I would have to spec out and special order from the internet. So I wondered - can I get one of the hydraulic cylinders and just use it with air instead of pressurized oil?
I don't know what stroke I need for the door yet, I haven't designed the system (custom retrofit deal). Probably the 2" bore 8" stroke would work, developing around 350 pounds of push maximum, probably use a bleed to control speed and a regulator to control push. Double acting so it both opens and closes. Skinner valves so it is electrically controlled. That sort of thing...
Brian
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1980 MCI MC-5C, 8V-71T from a M-110 self propelled howitzer
Allison MT-647
Tatamagouche, Nova Scotia
bansil
Full Member
Posts: 201
Re: Air vs hydraulic cylinders???
«
Reply #6 on:
March 22, 2013, 02:10:41 PM »
I wouldn't use a hydraulic cylinder for air,the big thing is volume vs pressure and sealing issues with air vs hydraulic the hydro cylinder is big and bulky and ugly....unless you need it
FYI a skool bus door opener (air) is a 5-3/8 stroke (atleast the 2 I have) with cleavice pin mounts and both ends are adjustible about 3/8 or 1/2 in and they allow a closed position to over 50* opening using the stock retro fitted mounts.
should be a $10 JY find
More is possible, if you optimize the angles etc.
As for strength?.. you cant push the door open when it's closed (i converted mine from folding bi-fold; to 1 pc swing open)
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Doug
Mnt City TN
Member of:
chessie4905
Hero Member
Posts: 7101
Re: Air vs hydraulic cylinders???
«
Reply #7 on:
March 22, 2013, 02:25:27 PM »
My ACFBrill had an air(pneumatic) cylinder on the door. It was ok, but check out these item/s on Ebay: 24 volt linear actuators in different strokes. 12 volt also. Reversible.
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GMC h8h 649#028 (4905)
Pennsylvania-central
Dave5Cs
Hero Member
Posts: 4667
BCM Subscriber
Re: Air vs hydraulic cylinders???
«
Reply #8 on:
March 22, 2013, 03:11:27 PM »
Just thinking that there are air over hydrolic jacks like the 20 ton ones most of us have. don't they work with air pushing hydrolic fluid.
Dave5Cs
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"Perfect Frequency"1979 MCI MC5Cs 6V-71,644MT Allison.
2001 Jeep Cherokee Sport 60th Anniversary edition.
1998 Jeep TJ ,(Gone)
Somewhere in the USA fulltiming.
Dreamscape
Dreamscape
Global Moderator
Hero Member
Posts: 3483
1968 Silver Eagle Model 01 8V92T Allison 740 #7443
Re: Air vs hydraulic cylinders???
«
Reply #9 on:
March 22, 2013, 06:26:00 PM »
They are two different animals for their specific application. Air works fine without a lot of load. Hydraulic is better and easier controlled. It really depends on your application.
I have used a lot of both in my previous life. Hydraulic is best for extreme condition, higher pressure and constantly lubricated. Best to control speed on the return side to maintain smoothness.
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______________________________________________________
Our coach was originally owned by the Dixie Echoes.
RJ
Vantaré Conversion "Miss Vivian"
Hero Member
Posts: 3938
Re: Air vs hydraulic cylinders???
«
Reply #10 on:
March 22, 2013, 06:35:58 PM »
Quote from: OneLapper on March 22, 2013, 10:45:58 AM
. . . I'm looking into the clutch assist thing too.
Mark -
Do you not have the "mousetrap" on your 4106's clutch linkage?
Properly set-up & adjusted, it makes the clutch as light as a VWs.
FWIW & HTH. . .
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1992 Prevost XL Vantaré Conversion M1001907 8V92T/HT-755 (DDEC/ATEC)
2003 VW Jetta TDI Sportwagon "Towed"
Cheney WA (when home)
kyle4501
Hero Member
Posts: 3882
NEWELL in South Carolina
Re: Air vs hydraulic cylinders???
«
Reply #11 on:
March 22, 2013, 07:33:33 PM »
Hydraulic cylinders are built heavier to withstand higher pressures possible with hydraulic fluid. If you add an inline pneumatic lubricator, a hyd cylinder should be fine with air.
Air cylinders usually have a very low "break away" force, so you should check the hyd cylinder to ensure it is acceptable. (Break away force = psi required to overcome the static friction of the seals.)
The real test is in connecting the hyd cylinder to compressed air & seeing that it moves as expected. Connect air to one port only & see if any leaks out the other port, if not, then you are good to go.
Let us know how it works out.
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Life is all about finding people who are your kind of crazy
Get your facts first, then you can distort them as you please (Mark Twain)
Education costs money. But then so does ignorance. (Sir Claus Moser)
Brassman
Sr. Member
Posts: 371
Re: Air vs hydraulic cylinders???
«
Reply #12 on:
March 22, 2013, 09:27:07 PM »
In a piston-in-cylinder actuator, the force applied equals the pressure on the piston multiplied by the area of the piston. Off hand I'd say that a hydraulic actuator used at normal compressed air system pressure would cost much more than a comparable air cylinder. The hydraulic cylinder would be designed for thousands of psi, not hundreds.
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hargreaves
1987 MCI 102A3
Sr. Member
Posts: 299
Re: Air vs hydraulic cylinders???
«
Reply #13 on:
March 22, 2013, 09:38:47 PM »
I have the air system of off the front door of my 102A3 you can have. You just have to pay the shipping from B.C. Cheers Gerry
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now as of Feb 2012 series 50 B400 . Sunshine Coast British Columbia
Darkspeed
Hero Member
Posts: 833
Re: Air vs hydraulic cylinders???
«
Reply #14 on:
March 23, 2013, 05:29:01 AM »
a Hydraulic piston as a door actuator seems very dangerous, you could probably create enough force to crush someone.
Look for a 12v actuator like
http://www.dcactuators.com/
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4106 6V92TA MUI + V730 8" Lowered Floor & Polished >
http://www.busconversions.com/bbs/index.php?topic=24673.0
QuietBox >
http://www.busconversions.com/bbs/index.php?topic=29946.0
It's all math and metal...
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Air vs hydraulic cylinders???
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