Hi Eric
The valve I am working with is not for a water heater as someone
mentioned above but for a well tank. The valve is quite smaller than a
hot water tank valve and very different. It basically is just a brass
fitting with spring inside(visible) and the opening is like a garden
hose fitting that is where the drip comes from. Dont think there is an
adjustment on this one. THere is s small piece size of dime that is
threaded in but doesnt look like it should be messed with. I can see
the explosion now hahaha
Should have seen me when I took it off. Turned off the 220v shut the
water off. Only thing is didnt think about the pressure tank needless
to say I took quite the shower and had quite a mess to clean

I know exactly what you have, I replaced mine earlier this year. The
cap on top is sealed off from the actual water, and there is a large
screw inside which tensions the spring. I tried screwing down my old
one but the seals were too far gone for the added tension to stop the
drip. My well guy quoted me ~ $50 for a new one, but I found one on
ebay for ~ $15. The new one held fine so I haven't adjusted it. I could
have rebuilt the old one if I really applied myself, but for that price
it wasn't really worth it.