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hydraulic spool valve

hydraulic spool valve

hydraulic spool valve

hi everyone,
i'm having trouble trying to work out what type of spool valve i have as the flow diagram is confusing me , after 2 days of trying to figure it out i have given up, way to confusing for me

the valve is operating a hyd motor , but it is working in both directions but according to the diagram should only be from PUMP TO A, have never come across a N port before , i presume it stands for neutral ? there is only four hose's and no power beyond.

any ideas anyone ??????????????

RE: hydraulic spool valve

I am going to guess that the letters are DA for double acting and NPT means pipe thread ports. And that the letters do not indicate Hydraulic function such as ports D, A, N, P, or T.
DA would be for double acting cylinder or reversible motor use.


RE: hydraulic spool valve

It is a 6 way, 3 position valve. The input side may be tank 1, pressure, tank 2. The output side would be ports A, B, C.


RE: hydraulic spool valve

hi , sorry picture not to clear ,the letters on top are B and A , so in centre position N port is flowing , with P / T / A /B closed, i presume that the relief valve is dumping back to tank.

in position 1 flow from Port N is being returned via Port A to Port T with P and B closed.

in position 3, Port P is going to port A every thing else closed but some how flow is returning as the motor is working in both directions .

i have no idea why such a complex valve is being used on a single motor !!

has anyone come across Port N before ???

RE: hydraulic spool valve

I found in a search Salami SPa shows an N port in their 6/3 valves. See their valves. Salami.it


RE: hydraulic spool valve

Well done Ted , looks like its a single acting spool with working port A. Have sent a email to try and find out how it works as it looks like it is multi adjustable by adding or removing blanking plugs .

RE: hydraulic spool valve

N is neutral

P is pump or pressure

T is tank

What is the motor driving? There is no drain back from the motor to tank when the spool is moved (to left as drawn), connecting P to A...so it is difficult to imagine what is going on down stream.

Pushing the spool in the opposite direction will drain A to T, but P is blocked...so is the motor reversing under gravity?

RE: hydraulic spool valve

hi Hpost,
the motor is a normal eaton t series 195cc, no drain of the motor, the motor is 100 % powered in both directions it is being used on a rope peeler with a catshead on the side and if i put rope on the peeler and tie the rope off to some where on the boat the peeler snaps 8mm rope in both directions .
just not sure how the N port is flowing in position 1 and how the fluid is returning in position 3

i starting to wonder if some one in the past has changed the spool !!! no one can remember any work being done on this valve for at least 5ys as the deck manager has been on for 5yrs . and has been working fine uptil now as the spool seals are leaking from old age wear and tear.
but the boat is out at sea for the 5days before i can get back on and check it. i think i will just replace with a standard tandem valve like a brand sdcf 755 tm 12. as i cant see any reason why this valve is being used this way.
the whole hydraulic systems on the boat are based on 12 gpm with 2000 psi

the peeler hauls rope from about 1500 ft from sea bed 150lb anchor with 100 or so hooks on,so when the uncliping the hooks the peeler has to hold the rope/line ie closed A/b ports . unclipping only takes seconds and each is spaced at 10ft apart.

the peeler is also used as a deck winch to raise and lower items from the fish hold, nothing too heavy but will lower and raise a 500 lb swordfish under control with no freewheeling etc

RE: hydraulic spool valve

The two ports at the bottom left are the P orifce. The lower right and the upper left port is T. And the 2 top right are the ports A and B.
The spool of this valve is used with A connected on a single-acting cylinder with a load that always go inside the stem. Example: forklift.
Then it is quite possible that your internal spool does not match the serial plate. To check: remove the hoses and blow with compressed air or cigarette smoke.
Best regards

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