Hydraulic Spool Valve circuits..

[Drains]

Luke, maybe a silly question, but why do you need to know?
I appreciate it would be interesting, even fulfilling, to know/understand how they work, but surely it's more important to know what they do?

Remember this is a schematic and doesn't show channel sizes,restrictions, other little features that go into the design of the valve.

Phone Harrier and ask. They make/repair/supply hydraulics. Then come back and tell us!

lol

Si

 

[Luke]

Luke, maybe a silly question, but why do you need to know?

Quite simply, because i want to.

I had spent time thinking about it quite a lot, before finding that schematic. I'm still thinking about it, and still searching for the answer.

The root of all this is eventually adding a hydraulic system to my range rover project - front and rear hydraulic winches driven from a crankshaft driven pump.

 

[Drains]

Quite simply, because i want to.

I thought that might be it... fair enough! I'd help if I could... I still recommend Harrier, or someone similar. I imagine, like me, you googled, wikipeed etc. Lots of single valve schematics but no banks that I could find, and certainly no explanations of banks. Ach well.
Best of luck. Let us know when you find out.

Si

 

[snowcat]

Il get me mate to nab one of the service manuals from work for a 360 or something might shed some light for you.

 

[Mith]

Luke, from looking at that diagram I think that there is a mistake and that port N should not be connected to the tank ports.
Port N is the carry over. It makes sense that the pressure can go straight through to there.
The only way that pressure should get to the tank is either through a cylinder, or past the relief valve.

In my mind, if the link between N and T1 was removed the valve would work. I cant see how that diagram works otherwise.
Otherwise, as you say, the pressure would always go around Y and straight to the tank (unless the spool on the right was pushed off centre.)
Thinking about it though, if N didnt go to the tank, then whenever you have all 3 spools in nutral the pressuer relief would have to open and put the pressure back to tank, which isnt how it works.


BTW, your circuit for your winches in unlikely to look like that. You'll probably want a valve for each winch, one running off the pressure carry over of the other.

 

[Drains]

To my tinily experienced eye that looks like a bells and whistles valve block. If you look at the pic on the pdf, it shows the 8 main ports with red covers, plus some(four?) others with chrome covers, which means they are optional. On most hydraulic actuators, you get an optional drain point which feeds back to the tank but is only used over certain pressures to account for internal leakage and to save seals from overpressure.

And the write up suggests options, like pressure carry over, hydraulic pilot option etc.This one does not have individual pressure relief settings for each valve. Others do.

I really think to understand in general how spool valves work, you need to find a simpler valve with a simpler schematic - like a three spooler with just 8 ports and no more.

Si

 

[Mith]

Si, the 2 that have silver covers on the top are pressure and tank ports, and are the same as the ones with red covers on either end. The silver covers are because they are plugged.
The other silver cover on the side is the pressure carry over port, or port N on the diagram.
Most valves do not have separate pressure relief for each spool. Some valves don't even have pressure relief.

I agree though, its easier to work out with a simpler valve, like a 2 spool one, with no carry over.
It looks like that valve is plumbed so that all 3 spools get equal share of the flow, that what that loop is for I reckon.

Luke, go to howstuffworks.com and try there. I recall they have an animation showing the basics of 1 spool operation. Didn't look hard enough to see if they had anything on multispool blocks though.

 

[Drains]

Yes Mith, I reckon you're right . I was about to reply to my own post re number of ports (multiple positional options seems to be de rigeur) and separate pressure reliefs (you can get them of course, but generally as you say, it's just the one). I've spent the past hour on the hunt and found no diags of multispools, but tons showing different types of singles.

This is the url for Harrier fluid power/flowfit's website. Lots of pdf's to look at here, lots of schematics.

http://www.flowfitonline.com/index.html

Si

 

[Mith]

I've been looking without luck too, just the single spool diagrams.

Just a FYI, Harrier seem to be about the cheapest out there. Go on eBay, you'll find them there. I don't know what their ram prices are like though, or if they do them at all, as I got those locally. Shipping on rams would be astronomical anyway.

 

[Drains]

I bought a few bits from Harrier last year - motor, check valve, overcentre valve and single spool. (Over-engineered the job a bit. oops) Deffo cheap, relatively, and the stuff works as it's meant to. The motor I got was shipped from Germany in a couple of days. I notice there are no motors in the online catalogue, but they are in the hardcopy (they were). I don't remember what rams there were, if any.

Shipping shouldn't be that bad. Theres no reason to pay more than £50 for a pallet or less from a supplier who moves plenty of gear. £70 for Joe Public without an account with a pallet courier.

 

[Luke]

Cheers for the info, I'll have a look at the Harrier site.

I get how a single spool works, its the banking of multiple spools that i'm interested in.

 

[guy88]

Right i did a MF advanced hydraulics course last week and that diagram is WRONG

This is one from an open centre system (closed centre is A LOT mor complex)

The port N should NOT be connected to tank. On the MF system The N channel goes onto supply a lube pump via a linkage controller.

Also the Flow divider only works on the first spool which gets priority over the others

the center block 7 is the important one as that joins the ports.

the way it is makes it so the spools have priority over anything else later in the system its all down to supply over demand

 

[Luke]

Thanks for that.