Pump design.

[ALIHISGREAT]

well this is my pump design which i need some advice on, firstly is the basic design satisfactory? i will be using 22mm copper as the body and 15mm as the shaft? will casting an epoxy piston be easy if i put the o-rings in the mold?

thanks Alasdair

and now for the hassle of insterting an image

[jackssmirkingrevenge]

make sure the head is designed in such a way to seal on compression but allow air to refill the chamber on the upward stroke, or have you decided to bypass this by including the extra check valve? If using this system make sure that at the bottom of its stroke there is as little dead space as possible, as this would limit the maximum pressure you can reach.

[Ragnarok]

well this is my pump design which i need some advice on, firstly is the basic design satisfactory? i will be using 22mm copper as the body and 15mm as the shaft?

That two check valve design is largely what I did for HEAL's pump, but I would advise against using 15mm copper as the shaft - it will bend really easily loaded like that and I assume you don't want that.
Get some 18mm or 3/4" PVC rod and use that instead, it will take the stresses much better.

I would suggest copying what I did and having a 28mm outer sheath for the pump body, which helps to protect the inner shaft both from bending, and possibly more importantly, denting. You won't regret it after a few months - some of the dents in the outer cover for my pump would have been the death of it if that had happened to the inner body.

I did write somewhere how I fixed everything together for the pump, which was carefully designed to minimise the dead space - I'll see if I can find it.

[ALIHISGREAT]

make sure the head is designed in such a way to seal on compression but allow air to refill the chamber on the upward stroke, or have you decided to bypass this by including the extra check valve? If using this system make sure that at the bottom of its stroke there is as little dead space as possible, as this would limit the maximum pressure you can reach.

yes i'm using the check valve to bypass that and how would you suggest getting little dead space?

That two check valve design is largely what I did for HEAL's pump, but I would advise against using 15mm copper as the shaft - it will bend really easily loaded like that and I assume you don't want that.
Get some 18mm or 3/4" PVC rod and use that instead, it will take the stresses much better.

I would suggest copying what I did and having a 28mm outer sheath for the pump body, which helps to protect the inner shaft both from bending, and possibly more importantly, denting. You won't regret it after a few months - some of the dents in the outer cover for my pump would have been the death of it if that had happened to the inner body.

so i need a 28mm body and a pvc shaft? maybe i could get my grandpa to cut some grooves for o-rings in some pvc rod on his lathe then i could use that as the piston.

[Hawkeye]

I'm not sure why you would want to complicate it with extra check valves. The floating o-ring is far easier to incorporate into the piston head and makes it much easier to eliminate dead space.
A copper pump rod is surprisingly durable. There is little chance for lateral pressure to bend it because the pressure doesn't build noticeably until the pump handle is almost fully depressed into the pump body.

[jackssmirkingrevenge]

how would you suggest getting little dead space?

By seconding what Hawkeye said

[ALIHISGREAT]

I'm not sure why you would want to complicate it with extra check valves. The floating o-ring is far easier to incorporate into the piston head and makes it much easier to eliminate dead space.
A copper pump rod is surprisingly durable. There is little chance for lateral pressure to bend it because the pressure doesn't build noticeably until the pump handle is almost fully depressed into the pump body.

hmm floating o-ring i will have to look think about that... but the reason i want to use check valves is that i think it would be more reliable (maybe) i will carry on thinking though.

edit: check valves are rated to 17bar looks like i will be using a floating oring and a homemade check unless the non-return valves on another site are rated higher.

[MaxuS]

They're rated for 17 bar, but I'm sure they'd work at much higher pressures quite well.

Why not put a Check Valve inside of the shaft?
You could compress the air already inside the pump body and allow new air to flow in on the upstroke.

[ALIHISGREAT]

They're rated for 17 bar, but I'm sure they'd work at much higher pressures quite well.

Why not put a Check Valve inside of the shaft?
You could compress the air already inside the pump body and allow new air to flow in on the upstroke.

thats a good idea ! i could have the air being drawn in up the shaft and encase the check valve in a piston with 0-rings or cast an epoxy piston with the check valve inside... hmm

[Ragnarok]

edit: check valves are rated to 17bar looks like i will be using a floating oring and a homemade check unless the non-return valves on another site are rated higher.

I'll let you in on a secret. The 10 bar ones work just fine for HEAL and the pump at over twice their rating. Sure, stick to the rating on pipe (especially PVC) but usually components will handle some extra just fine.
The 17 bar ones would handle just about anything.

@Hawkeye: I've seriously bent solid steel pump rods half an inch in diameter on a 160 psi pump (well, I was rather violently overpumping to somewhere above 200 psi). So, 15mm copper doesn't stand much chance - remember that UK metric copper is comparatively thinner in the walls than imperial copper piping. If it bends just slightly, the load is then not directly down the walls, and will serve to just bend it further. Copper pipe is even designed to bend, so it's not a good choice.

18mm or 3/4" PVC rod has the advantage that when it starts to bend, it has very little sideways movement because it's diameter is so close to that of the pipe it's moving in, so is totally impossible to bend past it's yield.

Floating o-rings are easy with a lathe, but they are still prone to going wrong. I've added all of 2 cubic centimetres of dead space by using a twin check valve arrangement, and it's more reliable. I'd personally recommend an almost direct clone of my pump to anyone that decides they want medium volumes at high pressure, and doesn't want to use gas bottles.

[MaxuS]

and doesn't want to use gas bottles.

I can't see why anyone would, they're a bitch when you want them refilled.
And of course, it's not free.
Homemade high pressure pump idea is much better.

Rag, where is the thread of your high pressure pump? I remember seeing it somewhere but can't for the life of me remember where..

[ALIHISGREAT]

Floating o-rings are easy with a lathe, but they are still prone to going wrong. I've added all of 2 cubic centimetres of dead space by using a twin check valve arrangement, and it's more reliable. I'd personally recommend an almost direct clone of my pump to anyone that decides they want medium volumes at high pressure, and doesn't want to use gas bottles.

ok i'm waiting for the design

edit: theres a whole thread on it ?!?

[jackssmirkingrevenge]

Simple and effective, I would pester Ragnarok for detailed instructions if I were you

[ALIHISGREAT]

Simple and effective, I would pester Ragnarok for detailed instructions if I were you

yes but i get enjoyment from pestering peope

and i would like to know a bit more about the piston and whats at the bottom becasue its obscured in the pic but i'm guessing tis a tee and two checkvalves then another tee with the guage on then the tube (where did you get it from?)

[Ragnarok]

There's a whole thread on it ?!?

Not yet, but I wrote a long list of how I did the pump shaft - which is the majority of the work. If only I could remember where.

Maybe I will make such a thread, along with one on piston valves. I've got HEAL's valve in bits right now for a rebuild of it to get more power from it, so I could take a few pictures along the way.

EDIT: That's more or less right - all the bits are from airlines, even the little springy bits at the ends of the hose to help prevent damage.