I picked up a hydraulic lift gate pump. It's 12vdc. The problem is using a single acting pump does not provide for a return, they traditionally activate single acting cylinders and bleed back through the pressure port.
When I get a chance I'm going to try to port the return into the vent port of the tank, and use a 3 way valve (center closed) for directing fluid to either lift or lower the cab.
The pump has a pressure control adjustment which allows to adjust the rate of lift. The pump will run and just bleed the excess back to the tank.
Many single acting units actually have a return port, it is just capped/plugged. Got pics Or model number? the good thing about the single acting units is they have a check valve on their output. Whatever you put on there has to have a check valve on the output for the hand pump to continue to function.
Coachgeo, he was talking about adding the return line, So I am thinking he is using the existing valve? You are correct you need pressure to pull the cab back over the balance point, but the restricted orifice in the valve controls lowering speed under gravity. If it didn't, the cylinder would lock.
In my experience most lift gate units are way oversized to run the LMTV system. Yes you can lower the relief pressure which will lower the load somewhat, but the electrical load is still a factor of flow rate@ set pressure. You are still paying electrically for 100% of that work even though 90% of it is passing thru the relief back to the sump...
Oh, and if you are running one of these larger power packs, I would definitely NOT do so while the engine is running/alternator online. the high amperage load these large units require is really hard on the alternator.