"RV" and "DRV" reliefs are differential poppet.
These have only a slight differential between cracking pressure and full flow pressure.
This makes them a good choice for mobile systems requiring a little more accuracy at the relief function.
The "RV" valve is usually used as a main system relief.
The "DRV" is a crossover relief used to protect overpressure in motor or cylinder lines.
Maximum flow is 30 gpm. Maximum pressure is 3000 psi.
Adjustment ranges are 500 - 1500 psi and 1500 - 3000 psi.
The "RD" relief is a direct acting ball/spring type. Fast opening and good for pressure spike relief.
Maximum flow is 20 gpm. Maximum pressure is 2500 psi. Adjustment range is 1000 - 2500 psi.