sorry it's taken so long to reply Tony.............. time very short at the mo.
The Bi-directional poppet [PB-S2I] is very low flow compared to PB-S2A.
both are specced for 3/8 port blocks, but S2I rated at 15 l/min [S2a 30 l/min] and 207 bar [S2A 240 bar]. This is cos they are Bi-Directional but we dont need that for dumps so its just unwanted restriction.
They would be OK to use in place of Lock Valves in low voltage systems but then you dont need 3 port blocks.