Injector pressure

[Dave M]

Screenman,
In another post you mention some injectors will push 250 lb. psi. How did you achieve that figure? I use GT' VP 5000 which has a pressure/vac dial, so I always know exactly how much pressure I am using. I think the LR hand pump does the same, not sure. Is there another way to measure pressure that I am not aware of?
When doing a bulls-eye repair I max out at 50 lb. psi, star breaks are about 40 lb psi. I can't imagine using 250 lb. psi.

[mrchip]

anybody remember the KIER system??? usually pumped to 60 and pushing envelope to 80..can't imagine 250

[screenman]

What we have to remember is that although I was talking about lb per square in. The actual size of the injector is far smaller than a square inch, therefore the pressures although real are reduced by that percentage. Therefore a 1/10 area would produce an actual pressure 1/10 of 250lb per square inch. If you look at a injector on the screen when you go onto pressure cycle it will sometimes lift the bridge slightly that is a lot of pressure when pushing resin into a crack. i am still trying to get my head around this. If your gauge reads 50lb in the large chamber does not the pressure increase when the resin goes into the smaller chamber, example the end of the injector. I do not know if I am explaining this well. As you all know my education finished when I was 15. A long long time ago.

If I am wrong on this I plead complete ignorance, that always gets me out of trouble.

[Nomad]

I believe that the air pressure will be equal throughout the system, if you have 50 psi at one place it will be that every where else. It's the same with hydraulics. It doesn't increase in pressure because of a smaller hole, it would just be a highter velocity if it were to escape from that hole. I think if you could put a 250 psi pressure on the injector and somehow keep it on the glass it would flow into the laminate and break the glass. I had this happen once when I put pressure on a spot that was already delaminated, the resin flowed into the space between the glass and broke it.

[screenman]

Just done a bit of physics revision. The formula f=pa applies here on our injector and many others the main resin chamber is larger than the piston chamber. Therefore increasing pressure in the main chamber depending on ratio of size will give a larger pressure in the smaller chamber.

We use a screw type injector and as we all know the pressure of a screw pump is far greater than many other types. My son is going to have a chat with his physics teacher today to see if we can find an easier way to explain this.

[Dave M]

Screenman,
Physics aside, I'm still curious how you arrived at the 250 lb.psi? Was a gauge used or did the manufacturer specify that was the maximum pressure possible with their equipment?

[screenman]

We use a Novus style injector and these numbers were produced by Novus using test equipment. As we are all quite aware we have a lot to thank Novus and Dr Warner for. I have no reason to disbelieve them. I am still trying to get someone more in touch with these figures and how they work to explain them.

[Dave M]

Thanks, Screenman