Aperiera,

In your last post you say “I really don't think (not saying is not) is a cavitation problem as the pump pressure is not high enough”

Cavitation is less likely to occur at higher pressures because liquids are prevented from boiling as pressure rises. That is why water will boil at a lower temperature as you climb a mountain, and at a higher temperature as you come back down again. Higher pressures and lower temperatures both help to reduce boiling and thus cavitation.

Cavitation is most likely to occur when pressure is reduced (as it is across the seat of a valve) or when the temperature is increased (which is why it is so important to reduce pump temperature).

As Arnstein has already mentioned in his last post, methanol (the major constituent or fuel) boils at 64.7 degrees C at normal atmospheric pressure. Nitromethane, the next most significant constituent boils at between 100 and 103 degrees C depending on its purity. The remaining oil in the fuel will have a higher boiling point still. Without doing tests, it is difficult to know at what temperature the fuel mixture is likely to start boiling. It would certainly be above 64.7 degrees C as Arstein has indicated, but it is still likely to be less than the levels of pump temperature that are likely to be achieved when the ambient temperature is high. That is why it is so important to do everything possible to reduce pump temperature, especially in that part of the pump where pressure is being dropped across the poppet valves.

I accept that there will be a small amount of hydraulic damping due to the regulator diaphragm, but it is likely to have little or no effect in respect to cavitation.

In summary, I believe that the reliability of the pump could be vastly improved by:

# Adding cooling fins to the poppet valve enclosure
# Increasing the diameter of the existing cooling fins on the pump cylinder
# Changing the material of the poppet valve seats from alloy to brass or steel (As Arnstein has already done)
# If necessary, changing the diaphragm material to cope with higher temperatures.

The first 2 of these modifications steps would also help the pump to cool down more quickly in between flights. And the good news is that none of the modification should add too much cost to the price of a new engine.

Regards

Bob