TheBigNasty

If you doubt the need for a needle valve then just try it. Infidel, of course, is dead on with his explination. As he said a 24v will buzz but the 12v will dang near blow the gauge apart.

Ram1999

I did as explained in a previous post in this thread. Needle is steady with ball valve wide open.

inline6359

Have you done a 12v? From the sounds of it it is a no.

wcbcruzer

Is it because the frequency of the pulsations from the injection pump is a lot higher than the response time of the gauge? Thus, stressing the gauge and blowing it?

infidel

On the 12 valve it's the mechanical lift pump that causes the pulsations. It's a diaphragm type pump, one stroke sucks fuel in, next stoke expels it. Envisioning this you can see how the pulsation develops. Without a dampener the needle will swing from zero to over 50 psi on each stroke of the lift pump, the faster the rpms the faster the swing. The needle valve slows the pressure change the gauge sees so what it is in fact doing is taking the average between the high and low psi.

zukota

1/8 Needle Valve Napa part number:

WH (weatherhead) # 6820