So I built a hydraulic pump today

[RCP57]

I've been messing with this(big mess, oil everywhere) a bit lately and I need some advice on the shaft seal. I've got the pump to produce around 12bar or 175psi without any trouble but the o ring(now 2) on the shaft can't take the pressure. I have tried standard rubber, Viton and harder rubber with no success. Does anyone know what the manufacturers use on this style pump? I'm trying to seal the 1/8 motor shaft. Pictures of any working set ups would be nice to see too!

Thanks, Reg

[Supermario]

Originally Posted by RCP57

My models are all 1/10 scale so they need a little more juice than most but I would be happy with this if it would make 200psi. My Volvo excavator runs over 425psi but it all depends on cylinder size and what you expect it to be able to do.

Thanks
Reg

Wow! 425psi! I never realized that some RCs run at that high of a pressure! That's close to pilot pressure on a 1:1 excavator

I don't deal with microscopic pumps like this at work but I know that to prevent pump cavitation a safe rule is 3:1 inlet size vs outlet. The fact that this is a gear pump a 2:1 ratio is fine just like Joe said 8mm inlet / 4mm outlet.

Any chance of using a lip seal for the shaft instead of. O rings? Do you have enough material to mill a bore for a lip seal? I can think of a few items that use a 1/8th shaft lip seal at work.
I'll see if they have one in the parts dept tomorrow, take a picture and send to ya.

Mario

[gauthib12]

great job on the pump, that is very good for a first go!! curious how did you seal the back where the motor goes?

Thanks,

[chaseracer]

impressive great job Reg!!!!!

[pugs]

Should be able to get quad rings that small.

[cdm]

it actually is rather scale......

http://www.cat.com/cda/layout?m=383895&x=7

Main System – Maximum Flow (Total) 232 gal/min
880 L/minSwing System – Maximum Flow 95 gal/min

Maximum Pressure – Equipment – Normal 5076 psi
35000 kPaMaximum Pressure – Travel 5076 psi
35000 kPaMaximum Pressure – Swing 4264 psi

we use 1 pump for everything (or in the usual case, electric motors)

if we scale that psi down to scale, say 1/14.5 that would mean

350psi main which is kinda in the league of vario. a cat 320 has the same pressure as a 374.. the flow varies.

however the flow should be 16 gallons a minute.. and it flows at what rate? around a litre! that's the part that isn't scale. because flow = big gears = resistance = power = big motors and big power drain.

now the other big thing is weight:

back to the 374 - Operating Weight 156819

in scale weight = 10815lbs


although my weight calculations could be wrong. not sure if scale weight is calculated any different than linear size

now keep in mind that models are made out of aluminum. if dense carbon steel is used, weight could easily be doubled or tripled. but that is a whole other mess on its own using steel

[pugs]

Volume doesn't scale same as distance

1/14th scale, 14 feet would be 1 foot, but 14 cubic feet would be .0051 cubic feet

So your scale weight example would be 57.14 lbs in 14th scale

[RCP57]

Thanks for the ideas guys. I did find a U cup seal on line in 1/8 so they are available. My local hydro shop didn't have any in stock that were 1/8 but said they could get them. They gave me the different O rings to try but didn't think they would work. I guess they were right. I guess I should make a new housing that has more meat on the back side. that would give me more room to install a proper seal. My Jung pump has a proper U cup seal but the shaft is larger too giving a lot more sealing surface. I'm wondering if the bushing in the motor is allowing the shaft to load one side of the O rings heavy when the pressure comes up. There always seems to be a little slack in these brushed motors but the original shaft length is long enough to use a support bearing on the other side. Maybe I should try that too? I put it back in the box and stuck it on the shelf because I was frustrated but I will get it on the bench again soon!

Reg

[WhiteWolf McBride]

Reg,

If you're going to try for a second edition/incarnation, and might want to dispose of the first, I might be interested, if it can handle water decently, as in a water-cannon pump.

I'd even be willing to send you my small Thunder-Tiger one that runs off what I think is a 180 (have to check it) as its unobtanium, and if you can replicate it at a decent price, I know guys that would ~kill~ for it.

Also, have you thought of running ssome of the oil thru the casing to cool it, and possibly thru a coil wrapped around the motor to cool ~that~... and if not oil, use a loop of water with some sort of a radiator.

WhiteWolf