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None of the Wagner pipe loaders had down pressure on the lift so you have no use for float on the valve. Flow rates were less than 10 GPM for the early models. If it is a hydraulic bucket a simple 2 spool valve DA is not expensive. An 8 GPM valve from surplus center is $150 plus shipping and will almost certainly do what you need. I'd buy it in a minute if I were in your shoes. Local suppliers can not beat the price....Prince 8 GPM DA 2 Spool valve
Plenty of other economical choices available from that source....