what type valve is needed for dump trailer cylinder raise and lower?

I have a Jinma 25 hp 3 cylinder diesel tractor with no rear hydraulics. I bought a homemade dump trailer which has one cylinder. The man who sold it to me said he only hooked up one of the hydraulic fittings on the cylinder to his tractor's rear port and after he raised the dump bed to dump, he would just release the single lever and let the cylinder decompress back to the closed position. A friend who works on diesel machinery said I would need an open center valve and that Tractor Supply sells a SBA 4 valve that would work for my needs. The folks at Tractor Supply don't know what else I would need to make the connections. Can someone in the forum tell me what I need? I posted this before and got a response from a company that makes these up but the cost was $550.00. I need to keep this at half that cost.  Anyone have what I need for a price I can afford? Thanks. Mickey Paul