Go BottomFord 1700 HV5902Adaptor block
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2025-08-05 201910
Have a No. HV5902Adaptor block to mount between relief valve v e and housing. Have no instructions plus none of the three passages were bored through on block. At this point I believe the top port of the front two to be my pressure and connect to spool port p. The bottom of the front two to be pressure to 3pt valve and fed by PB of spool valve body. The rear port -sump return. This port is not accessible due to not Have been bored to exterior of adaptor or tapped for fitting, so T of spool body will go to a plug in housing. With no literature for adaptor , could someone please confirm or rebuke my analysis
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Add PhotoFord 1700 HV5902Adaptor block
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2025-08-05 201911
You're describing a No. HV5902 adaptor block that's intended to mount between a relief valve and a hydraulic housing—possibly on a compact utility tractor or similar application. From what you’re saying:
The block came with no documentation.
None of the three passages are bored through, which is unusual.
You're trying to identify and correctly connect:
Pressure input (P)
Power beyond (PB)
Tank return (T)
⚙️ From your analysis:
Port Your Assumption Purpose
Top front port Pressure in Connect to spool valve P port
Bottom front port Pressure out (PB) Feeds 3-point valve, comes from spool PB port
Rear port Sump return Should go to spool T port, but is not drilled or tapped
Your interpretation seems mostly correct, and it sounds like the block was left unfinished—perhaps a casting blank or machining error.
✅ Let’s walk through a typical adaptor block flow for a loader valve:
Pump pressure (P) enters the block from the tractor.
Block routes pressure to the loader spool (P port).
From the loader valve's PB (power beyond) port, pressure is returned to the 3-point system (so it still works after loader).
From the loader valve’s T (tank) port, low-pressure return oil goes to sump through the block.
If the rear port is intended for return to sump, but it hasn’t been drilled or tapped, that breaks the circuit. It explains why the T port has nowhere to go and why you’re planning to plug it at the housing.
❌ Caution:
Plugging the T port of a spool valve is typically not safe unless it’s an open-center valve and you're 100% sure all return oil is going out the PB line. Even in that case, you must:
Use a power beyond sleeve/plug in the valve body,
And route PB to 3PT, with T going to sump.
If you plug T and there's no dedicated sump return, you’ll risk:
Blowing internal seals
Deadheading the system
Overheating fluid
Dangerous pressure spikes
🛠️ Options You Have:
Modify the adaptor – Drill and tap the rear port to make it functional for return to sump. This is the proper solution and restores the normal hydraulic circuit.
Replace the adaptor block with one that is correctly machined.
Route T to another available sump return (e.g., transmission case drain or rear remote return) only if factory guidance confirms it is safe.
🔍 Can You Share:
What tractor/model this is for?
What valve are you using (open or closed center, power beyond capability)?
A picture or sketch of the block?
This would help lock down a safe and accurate setup.
✅ Summary of Analysis:
Your interpretation of:
Top front port = pressure in
Bottom front = pressure out to 3PT
Rear = tank return
...is reasonable and consistent with common hydraulic adaptor blocks. The real problem is the rear port being unfinished. Without that, your return oil has nowhere to go. Plugging T is not safe unless your valve is specifically designed for it, which is uncommon.
You’ll need to either:
Drill/tap the rear port to complete the circuit, or
Replace the adaptor with a properly finished one.
Let me know the tractor and valve model if you want help verifying port assignments.
....
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