Anyone here that can tell what the usual flow ratio between A port and B port on a std directional valve. A port usually is little more spaced inside valve. Maybe some links to more info?
Thanx for a great forum

This catalog information from BoschRexroth shows pressure drop across the different flow paths in a tpical 4-Way DCV.

Is this what you are asking about?
http://www.boschrexroth.com/Rexroth-IHD/Home.cfm?Page=RDSearch&Filter=23327

Look at catalog n23327 (English) and find the page showing Pressure Drop through the valve with all types of spool configuration.

See my picture
I have seen valves with more spaced core in the iron cast on A port side(red)than B port side (green)
I worked in education and "opened" valves with milling machine to show cores inside, spool types, over lap, etc. It was a long time ago and it was old valves....Maybe everything is customized in the spools today?

The valve cutaway you show is the type used in Mobile Applictions with multiple functions and usually a Fixed Volume Pump. There design is unique in several ways and have some great features that are not available in Industrial type valves. Try to find some material from Gresen, now ParkerGresen, and look at their training material. They go through all the features of this design and how they can be applied. Commercial Shearing and others make these valves also.

The way they are made is completely diferent to an Industrial type valve though they both may be designated as 4-Way valves.

I have worked very little with Mobile type valves and that is the reason for the link to a Bosch-Rexroth catalog in my previous post.

Thx Bud!
My experience is all mobile, since mid 70's till I retired at 2000. And it's mostly from scandinavian logging equipment like Volvo BM, Valmet, Timberjack etc. forwarders, processors and harvester heads etc
I'll keep research'n

Some servo valves are cut differently to account for the difference in flow in/out the closed side vs the rod side area. A symmetrical valve in & out would have different pressure drops in & out due to the difference in areas.
That could cause issues with overrunning loads, and decelerations.
If you go through jack johnsons VCCM equations, (steady state, not dynamic conditions) the presures across the lands in & out will show the reasons in more detail.

Valves cut like that are typically 2:1 or 1.5:1 or something. They must be connected to the cylinder in the correct polarity.

k

quote:

Originally posted by kevin j:
Some servo valves are cut differently to account for the difference in flow in/out the closed side vs the rod side area. A symmetrical valve in & out would have different pressure drops in & out due to the difference in areas.
That could cause issues with overrunning loads, and decelerations.
If you go through jack johnsons VCCM equations, (steady state, not dynamic conditions) the presures across the lands in & out will show the reasons in more detail.

Valves cut like that are typically 2:1 or 1.5:1 or something. They must be connected to the cylinder in the correct polarity.

k

Thanks Kevin
This is the answer I'm looking for 2:1 or 1.5:1...
Do you know this is common on mobile valves today? for example lets take a simple 1 spool hand operated 3000psi 10-20gpm
If I look on data sheets on valves it dont say anything about it, but I would like to find a valve like that...

Thanks again
gr8 answer
P

I don't believe you will find a Mobile valve with an asymetrical spool of any percent flow difference.

You could modify a standard valve by limiting the spool travel mechanically in one direction but that would mean a special that would work until someone without knowing the special feature replaced it with an unmodified valve.

I also doubt any common valves are available that way. It doesn't matter on open loop manual control anyway, as the pressure drop through the valve is much lower compared to the load pressure.
bud: the spool cut is different than just stroke limiting in one direction. stroke limiting reduces both lands in & out by say the 50%. The spool cut is like having a 3/8 orifice going into the closed side, and a 1/4 orifice coming out of the rod side. With the difference in flow rates/area ratios in and out, the pressure drop across each set of lands comes out roughly equal. It is most often done with overrunning load in rod extend direction (either overrunning by gravity down, or by decelerating a heavy inertial load). If the lands were equal, the pressure drop on the inlet to closed side would be higher, the outlet out of rod side would be less, and the closed side inlet could cavitate or lose control. Sort of like meter in control, it could cause too much pressure drop on the inlet compared to the deceleration pressure drop at the outlet.
Look at it like a meter in control on the one lands, and a smaller meter out control on the outlet lands.

but again, I don't know of any mobile valves cut that way, or why necessary. They usually have overlap, especially with the load checks used with most mobile valves, such that there is not muchmeter in control. The control is done bymetering out of the cylinder in whichever direction it is.

The Sauer-Danfoss PVG 32 series mobile proportional directional control valves are available with asymmetrical spools. The spools in the catalog are all symmetrical, but S-D has released hundreds of combinations of flow rates, they just don't publish them in the book. They also make "pressure control" spools, which can be very useful in some hydraulic motor applications (slewing a crane, for instance).

Bill O'Donnell

The Sauer Danfoss KFB? and MCV valves for pressure control are unique: they use two separate spools, one for C1 port and one for C2 port. The pilot pressure circuit is symmetrical, and the second stage spools can operate individually to create the same output pressures as the pilot stage, but at different flows in each side. We have used them in a force control circuit for many years with great results. More stable pressures and less cavitation effect with gravity down. The one spool opens much greater to keep the same desired port pressures.

k