SpudFiles

Does anybody here has a hatson pcp pump? I heard some bad things about them but good things too. Basically it´s said that their o-rings wear out pretty quick, but they looks pretty good to me. The one I found it´s about 10 euro cheaper than a hill pump, the price isn´t really important, I prefer the look of the hatson, but the hill pump has a good reputation and the o-ring replacement it´s easy to find. Any thoughts?

Around here at any rate....the Hill has a good reputation, and parts are readily available...get the pump too hot, and you'll scorch an o-ring...and need the parts.

Hill is also the ONLY manufacturer I've heard of that encourages owners to rebuild their pumps.

IMNSHO...get the Hill.

Yap, I was decided on the Hill as well...
Also I decided to use 440c stainless steel for my chamber, 0.15 inch wall, sounds ok? I did several FEA simulation about it, seems good.

Does any one knows how does a airgun magazine works? The revolver style one. I wonder how does they rotate automatically when the bolt is pulled and only turns a little bite to the next pellet and locks there
thanks.

Thank you! Wow I can really find everything here

when brazing cast iron to mild steel (fitting to pipe) no post heating is required as long as i don't get it to hot correct? Also would brazed joints be suitable for a low mix hybrid (up to X4)?

Thanks.

kydavies wrote:when brazing cast iron to mild steel (fitting to pipe) no post heating is required as long as i don't get it to hot correct? Also would brazed joints be suitable for a low mix hybrid (up to X4)?

Thanks.

I don't think you would need to post heat treat. Keep in mind,though, that the yeild strength of the steel and iron decreases in the heat affected zone. You would "un-do" the work hardening from the possible drawing of the pipe, as well as any previous heat treating.

You shoudl still be fine for 4x at reasonable diameters. Soldered copper is, IIRC, rated to ~3ksi working, and steel/braze is much stronger than that.

ramses wrote:Soldered copper is, IIRC, rated to ~3ksi working.

Uhh, no.

Shard, thanks for the chart. I cant read all of it right now because my computer is retarded but i can assure you i will. No pun intended if I brazed the but joint and get full penetration it should be fine for metered propane and low mixes (building a metered combustion with hybrid capabilities)

shardbearer wrote:

ramses wrote:Soldered copper is, IIRC, rated to ~3ksi working.

Uhh, no.

aaah, I think failures is at 9ksi, so we used a safety factor of 3 for the calculation. thus the "IIRC" part

2" pipe fittings are "rated" to 125-150 psi, but have been used consistently at nearly 2ksi.

Okay, so there's a few decent quality fridge compressors coming my way soon for spudding purposes. I've read the threads here on the subject, but one question remains.

Fair enough theoretically adding a small amount of pressure to the inlet of the fridge compressor will result in that x the compression ratio of the pump out, but how can it provide more output pressure than it would be able to by inducting air at atmospheric pressure? assuming there is a fixed amount of torque the motor/flywheel/crank can provide?

The only reason that springs to mind for this is that the pressurised air coming in is applying additional torque to the flywheel on the inlet stroke and that's what allows it to achieve a higher max outlet pressure.

Just something i was curious about if anyone could help out with an explanation

My fridge compressor reaches 1000 Psi with no input and just over 1500 Psi with 30 Psi room temperature air input, theoretically you could create your own piston assembly from stainless steel and use Urethane o-rings and hook it up to a washing machine motor with a gear system to create huge torque.

The bottom of the piston in a fridgepump is exposed.
The higher the inputpressure, the higher the force on the bottom of the piston.( and the top too ofcourse!!)
This means that the motor can compress the air to a higher level before it cuts out.

Think of it as lifting a weight with a teeter-totter.
You're on one end trying to push the seat down while there is a 50 pound weight on the other end.
You can probably do that with one hand..

Now add 300 pounds on both ends.

Suddenly you are able to lift 350 pounds with one hand!!

This is all that the pressure input does.

Eventually, something will give.

One additional thing to consider is that you are also now pumping ~3x the air through the compressor per stroke, since it is now pre-pressurized to 3 atmospheres (absolute), rather than 1. The motor will be more loaded, and will require more force on the arm early in the crank cycle, where the motor has less mechanical advantage.

In short, you will be more likely to stall your fridge compressor, and less likely to get to the point where the dead space in the pump is limiting the outlet pressure.