Spool valve problem


We have Kontak spool valve block on our old Bomford B428? Hedger.
When extending Rams it's fine. When retracting Rams you can hear the tractor straining and it's slow as if there is some kind of restriction, even when Gravity is helping the ram to close.
Open centre hydraulics. Same happens on two different tractors so don't think it's the tractors hydraulics.
We have fiddled about with control cable adjustment to adjust travel of the spools but it seems to make no difference.
Blockage in the spool block? Or is it normal?
Next step is to dismantle the spool block but thought I'd ask before doing that. Thanks.

Mr Happy

Before you dismantle the Kontak spool valve try swapping the two double acting services over as the fault is with the double acting ram. If the fault then moves to the other ram its a spool valve fault, if it stays with the same cylinder its a ram fault. You have already eliminated the tractor as you have swapped them over. Also have a look in the spool valve adaptors because some of those act as flow control valves.


Thanks. I will have a look. Both double acting rams struggle to retract (one which is the outermost ram which is lifting the flail head, the other which is lowering the arm connected to the rotor. They extend without a problem.

I will check for blocked restrictors. Sounds like it.

Oil seems to circulate freely round when no ram is operated and there is no straining when Rams are extended so I would have thought it unlikely that the quick connectors are causing the problem but can't rule it out.


South Devon
Rams extend without a problem.
That's because some of the circulating oil is going to extend a ram so less is being returned to the tractor.
When you retract a ram,oil is displaced by the piston ,so extra oil is being returned to the tractor.

First of all check oil is circulating the correct way through the Kontak block.

Then try returning oil through a pressure free return.

Its quite possible that the gpm of a modern tractor is too much for the 3/8" return hose ,so replace with 1/2"


It's correct way through Kontak block.
I agree that ram extending means a net output of oil.
Retracting ram means a net additional return of oil but not much as the ram is double acting so some oil is pumped to other side of piston, although I agree more returns from the retracting side but not a massive amount in the scheme of things.

Tractors are DB1394 and Case IH4240 fairly elderly and wouldn't have thought major flow.

We did fit a straight through return for the Browns post knocker as we found the quick release connections closed when the hammer dropped but this still went through the tractor spool without a problem and it was major flow.

I will look at any flow restirictors in the ram / valve piping next. Thanks.

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