Hydraulic Valves

The two main types of high-performance hydraulic valves are:

  • Servo-Quality Proportional Valves
    Also called high-performace proportional valves. These are more common. Make sure the valve has a ±10V command signal (not 4-20mA).

  • Servo Valves (current driven)
    Flapper-nozzle, or jet pipe. Often called just servo valves, these require a current input, such as ±50mA. To use these with an RMC, a Current-to-Voltage converter is required, such as the VC2124.

Servo-Quality Proportional Valves

For great performance, trouble-free set-up and machine operation (this means lower startup and maintenance costs), Delta recommends using linear valves with a zero-lapped spool and on-board electronics.

The RMC75E, RMC150E and RMC200 do support non-linear valves (with a single “knee”), but it requires extra set up. A linear valve is the easiest to use.

Linear Valve:
This means the flow vs command signal profile is linear (at least up to about 8 volts):
Terms such as “kink”, “knee”, and “progressive” indicate a non-linear valve.

Zero-lapped spool:
This means the spool is cut so that as soon as a voltage is applied to the valve, hydraulic fluid starts flowing.

On-board electronics:
This means you don’t need to wory about a separate card, and typically, with a good valve, you don’t need to make any adjustments on the electronics.

Important Notice
If you enjoy headaches, choose a valve with an overlapped spool (we call that deadband), and a non-linear flow versus command signal profile. Notice, however, that headaches can result in costs savings. Especially for OEM applications, where you just need to go through the difficulty once, and then pump out volume, it can be well worth it to get a valve that is barely good enough to do the job. On single applications, the time savings in setup usually justify a good valve.

Recommended Servo-Quality Proportional Valves
Here are some valves that Delta knows have been used successfully. Many valves offer +/-10V or 4-20mA input. Make sure to choose +/-10V.

DLHZO-TEB and DLKZOR-TEB: single-stage, sizes NG6 and 10. The first L in the part numbers indicates a sleeve, which gives more precise control and faster response.
DPZO-LEB: two-stage, sizes 10-35
The EB indicates the Basic Integral digital driver, which is all that is necessary when using the RMC to control the valve.
F180.pdf (1.54 MB)

Bosch Rexroth
4WRREH: Size NG6. Very fast response. Make sure to choose the ±10V command option.
4WRPEH: Sizes NG6 and 10. The NG6 is not as fast as the 4WRREH, but still good. Make sure to choose the ±10V command option.
4WRLE: Sizes 10-35. Make sure to get the V spool with the L (linear) flow characteristic.

VED03MX: Size D03. Very fast response.
This valve is quite linear, but not perfectly so. Setting the Velocity Feed Forward for a large command voltage typically results in the best tuning.
The VED03MK is not as high performance as the VED0M3X, but will also work quite well.

Axis Pro valves are very high response and work well for position control, but we have had several reports that they are not suitable for pressure or force control. D03 and D05. Choose level 1 in order to work with the RMC. Make sure to choose the ±10V command option.
K(B)SDG4V-3: http://www.eaton.com/ecm/groups/public/@pub/@eaton/@hyd/documents/content/pll_2105.pdf

D661: Very fast response and high flow.
D681-D685: Very fast response and high flow.
D633/634: http://www.moog.com/literature/ICD/Moog-Valves-D633_D634-Catalog-en.pdf
D636/637: http://www.moog.com/literature/ICD/Moog-ServoValves-D636_D637-Catalog-en.pdf
79-series: Crazy high response for 200 gpm (750 lpm)!

Very fast response valves with great control.
D1FP: Size NG6. Make sure to choose the ±10V command option.
D3FP: Size NG10. Make sure to choose the ±10V command option.
These valves are quite linear, but not perfectly so. Setting the Velocity Feed Forward for a large command voltage typically results in the best tuning.
The D1FH is not as high performance as the D1FP, but will also work quite well.

Santest DA03S
As of this writing, Santest offers only this one valve, a D05 size, with or without on-board electronics. It is possibly the fastest valve we have tested, and provides exceptional control. The fastest response requires a 48 VDC power supply, and it also supports 24 VDC. The testers say this valve may be the easiest tuning valve they have tried. It tuned a cylinder in pressure control unusually easily. Pressure control is where the differences between valves becomes more pronounced.

Star Hydraulics
Star primarily offers high quality servo valves.
200: Delta has used this valve. It is very small in physical size, 7 lpm, performs well and needs a current output. The VC2124 or RMC200 CA4 module can provide current for this valve.
Make sure to choose a linear zero-lapped spool. If you have a very fast application, choose the high response version.
Most of the sero valves take a current input. However, some of the servo valves have on-board electronics. In this case, choose the ±10 volt option.

The LSVG-01-EH and The LSVG-03-EH are crazy high response and linear with on-board electronics. D03 and D05, but maxes out at 60 lpm. Make sure to choose the ±10V command option. Yuken also makes a similar high response D05 valve, the SE1024, with more flow, 130 L/min. In addition, there are two-stage valves with very high flow (up to 3800 lpm) and very fast 0-100% step response (8-13 msec).

For more details, or to suggest a product to be added to this list, send an email to support@deltamotion.com.

Is there some reason why the Rexroth 4WREE valves are not on the list? I know I have used them in the past but maybe my applications weren’t very demanding…

The 4WREE valves have a much slower step response, lower bandwidth than the valves we recommend and therefore will not perform as well. Also, they have a curvilinear profile which requires more work when setting up and tuning the axis. That said, there is always a tradeoff between cost, performance, and time to setup. If the precision requirements aren’t so high, the 4WREE may work just fine. If it is a high-volume OEM application, it can often be worth it to spend more effort trying to get the least expensive valve to work.

There is another “gotcha” with certain versions of the 4WREE Bosch Rexroth valves. This is with the 32L NS6 valve and the 75L NS10 valve.

They are flow limited at higher pressure drops. What this means is that the Bernoulli forces within the the valve become stronger than the solenoid force and the valve begins to close which wreaks havoc on the control loop.

This has bitten a lot of people and it is counter intuitive so unless you have come up against it or someone has told you about it, it can be very confusing and frustrating.

Like Jacob said, for the right application it can be worth the cost savings and we have used a lot of them successfully but you have to stay away from those flow limits.

I see now where the 4WRPEH valves have <10 ms response from 0-100% command whereas the 4WREE is about 40 ms.

Ndzied1, I have seen that max flow line before on other valves but didn’t know/remember that it specifically applied to some of the 4WREE series. I think it is also there on some of the “bang-bang” stuff. Good info.

Sometimes I wish I had more (read: formal) hydraulics design experience, especially in selecting valves and pumps.

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