Using Kontak spool valve as closed centre type.

[Sion.Dovey]

I wonder if it is possible to convert the standard 1/2" Kontak spool valves to closed centre for use with a load sensing piston pump? Also, my purpose will mean stringing alot of valve slices together, possibly as many as 18 in one block, is there a problem with having that many in one block? - the machine is unlikely to need more than two services to be used simultaneously.

I hope someone can help - i havent been able to find good info on the kontak spool blocks online, but ive chosen to try to use them as i have nearly enough slices to make the block up in my 'useful spares' collection.

 

[john432]

Is there a limit to how many spool slices you can join due to the force pushing the slices apart greater than the tensile strength of the securing bolts? Not sure?

 

[Sion.Dovey]

I didnt think that the clamping force multiplies up like that, but i may be wrong there. I thought there might be a problem with the block growing in length when it warms up, but that would be easy enough to solve.

I dont need to run a very high pressure, 170 bar should be plenty.

 

[Nearly]

@Mr Happy

 

[Mr Happy]

Very sorry but you can't convert a Kontak valve so it can be used with a load sensing tractor. The best valve would be a Danfoss PVG32 valve but not with 18 work sections. Using a PVG32 will allow you to operate two functions at once. Also you can operate the valve either manually, electrically or hyd pilot.
I am very interested in what kind of application requires a 18 section valve.
If you are looking for info on line Kontak is now owned by Parker Hannifin.

 

[Sion.Dovey]

Very sorry but you can't convert a Kontak valve so it can be used with a load sensing tractor. The best valve would be a Danfoss PVG32 valve but not with 18 work sections. Using a PVG32 will allow you to operate two functions at once. Also you can operate the valve either manually, electrically or hyd pilot.
I am very interested in what kind of application requires a 18 section valve.
If you are looking for info on line Kontak is now owned by Parker Hannifin.

Thank you for your reply, im interested to understand why i cant convert a kontak valve to closed centre? I suspected that might be the case but i dont have any experience with closed centre hydraulic systems. Also, thinking since my post that if i go for the closed centre option, ive realised i dont need to put all the valves in a single block because i can put more than one valve block in parallel with a closed centre system (not certain im right about that either). That would be nice because i can make separate blocks up more sensibly mathed to areas of the machine - that coukd be a bit more intuitive to use.

The ultimate purpose is a sawmill, its all electric pneumatic nonsense at the moment but i am converting it to more dependable good old mechanical hydraulic controls. Pump is probably to be a parker pv140 which i have, max output turned down a little bit and turning about 1300 to 1500 rpm.

 

[Mr Happy]

That's ok if I can help I will. You can't use the Kontak valve with a load sensing pump but you can convert it so the valve is closed centre like you need when it's fitted to a John Deere tractor. The reason is Kontak don't supply the inlet cover with s LS port which sends a signal to the pump. If you have the full pump code we can check what specification you pump is and see what spool valve specification you require.
It sounds like a very interesting conversion you are planning.

 

[Sion.Dovey]

That's ok if I can help I will. You can't use the Kontak valve with a load sensing pump but you can convert it so the valve is closed centre like you need when it's fitted to a John Deere tractor. The reason is Kontak don't supply the inlet cover with s LS port which sends a signal to the pump. If you have the full pump code we can check what specification you pump is and see what spool valve specification you require.
It sounds like a very interesting conversion you are planning.

Thank you, i thought that the pressure sensitive flow control was contained within the pump and doesnt require a separate signal line from the valve block? Is that how the john deere system works? Could you describe how the kontak valve is converted to closed cente for use on a john deere? I have two types of end plates for kontak blocks, one type pair with a blank end and both in and out ports at the other end, and the other type with flow and return at opposite ends. The only experience i have here is with an open centre setup but mistakenly connected the wrong way round and i remember weird stuff happened, the spool valve worked sort of ok but under higher pressure the levers became stiff to use so there must be some problem with back pressure at the T port which made me think it wouldnt be possible to use a kontak valve as closed centre, but i have found a couple of references to them being used as such hence my original question.

Without getting in too deep im going to use the kontak valves because i have enough of them and purchasing enough of something else just to chase the closed centre option would be prohibitive for me. My plan A was to use them in a single 18 slice block open centre and work out a way of controlling the pump flow control manually, i have good reason to go with that option and had largely worked out the details for it but i had the plan B closed centre idea recently and thought it worth some research.

 

[Tractortech]

Now Then..
As far as I know there are now 3 types of hydraulic systems.
1 - Open Centre, where the oil flows continuously in an open circuit. Used by most tractor manufacturers way back with a gear type pump.
2 - Closed Centre, where the centre of the valve is closed. Pressure builds and pushes the radial pistons away from the driven cam in the centre of the pump which stops pump flow but at high pressure. Used by John Deere up to the 50 series which ended around 1992.
3 - Closed Centre Load Sensing (CCLS) as used in many modern tractors. This needs a sensing line back to the axial piston type pump to move the swash plate thus making the pump send oil to the service.
A Kontak valve is easily converted from open to closed centre and will sort of work on CCLS but has drawbacks.
In closed centre, the pump is in high standby and the oil gets hot.
In open centre, the pump flows oil at full flow low pressure until a service is used when it has to react suddenly with back pressure issues..
There may be more to it than this.
If you leave it as open centre with a cheap gear pump you could run as many valves as you like in banks connected in series,,,,,, perhaps
Someone else may know better about that..

 

[Mr Happy]

Many thanks @Tractortech for answering the above questions, saved me a job. The way Kontak convert there valve from open to closed center is the valve end cover, the tank port is blocked.
You would be best in my opinion to use an open center pump but if you want to locate the valves in different areas rather than a massive spool valve, you will need to have the valve built with pressure carry over ports.

 

[Sion.Dovey]

Thanks for all the help above, theres still a couple of points im not quite clear on -

I have a pressure compensated flow pump, which in my very basic understanding of closed loop hydraulics is different from a load sensing circuit, there is no LS port or any ports other than inlet, an outlet, and a case drain on the pump housing, so im assuming the pressure compensation circuit is entirely enclosed within the pump body - can i convert the Kontak valve block for use on that type of closed loop system?

 

[Sion.Dovey]

Here are a couple of pairs of kontak end covers i have. the first one is i think hiding a carry over port behind that bung. Ill find a few more shortly...

 

[Sion.Dovey]

Another pair, this one seems to have no relief valve?

 

[Sion.Dovey]

This block is busy, but ill find a solution to replace it if its relevant to my current project. It looks to have the carry over port in place to feed onwards to a power steering circuit.

 

[Sion.Dovey]

I have a few more, but they look to be duplicates of some of those above, externally anyway. Hopefully something in what i have above is relevant to converting a kontak block to closed centre for use with the pressure compensated pump that i have?

 

[Sion.Dovey]

Reading back through i can see where i went wrong with my very first question in saying i wanted to use it with a load sensing pump, i now realise that was a completely wrong description and my thinking it was the same as a pressure compensated pump was a result of my minimal knowledge of this type of circuit - im really sorry for the confusion.

 

[335d]

The ultimate purpose is a sawmill, its all electric pneumatic nonsense at the moment but i am converting it to more dependable good old mechanical hydraulic controls. Pump is probably to be a parker pv140 which i have, max output turned down a little bit and turning about 1300 to 1500 rpm.

interested to know why you would want to convert electro pneumatics to hydraulics? In my experience electro pneumatics are very reliable . Surely changing all the cylinders, valves and pipe work will be a huge expense.

if you don’t like the electrics parts, then change the controls to manual pneumatics.

 

[Sion.Dovey]

interested to know why you would want to convert electro pneumatics to hydraulics? In my experience electro pneumatics are very reliable . Surely changing all the cylinders, valves and pipe work will be a huge expense.

if you don’t like the electrics parts, then change the controls to manual pneumatics.

Compressed air is comparitively expensive to run, both energy wise and wearing components in the compressor, the quantity required would entail probably a 30 hp compressor running constantly, and that doesnt cover all of the necessary operations, a fair few are already hydraulic and currently run by two 3 phase gear pumps, totalling 25Kw, and controlled by solenoid operated valves, mechanically operated hydraulic systems are much easier to troubleshoot, and by combining that with a variable delivery pump, which if it works as i imagine will work far more efficiently. The machine should see me out so the potential comparative running costs over years stretching into decades are a much more important factor than initial setup cost.