# Controlling a Proportional Valve

Discussion in 'The Projects Forum' started by Mike Webb, Mar 4, 2016.

1. ### Mike Webb Thread Starter New Member

Mar 4, 2016
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I have come across several systems that monitor the Hz from an AC alternator which in turn sends a dc signal voltage to a proportional valve on a hydraulic circuit to maintain a constant flow rate / rpm such that the Hz from the alternator remains fairly constant. I am sure there are control circuits already available that will do this but I can't find anything, can anyone offer any advice.

2. ### wayneh Expert

Sep 9, 2010
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Do you know what the proportional valve needs as a control signal? Maybe a voltage? If so, a simple approach would be a frequency-to-voltage converter such as you can make with a 555 timer IC. If the valve needs a digital signal, that call for something else.

3. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Welcome to AAC!
How does controlling flow rate also control an alternator's rpm? What is driving the alternator?

4. ### shortbus AAC Fanatic!

Sep 30, 2009
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Isn't this usually done with a mechanical pressure regulator? Sizing the pump for the lowest used motor RPM and the pressure regulator controlling pressure at higher RPM's.

Jul 18, 2013
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All the proportional valves I have come across usually requires some kind of feedback in order to implement a PID loop, otherwise the control is rather crude open loop?
Max.

6. ### crutschow Expert

Mar 14, 2008
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I assume the alternator is being driven by a water turbine and you want to adjust its flow-rate(?).

For that I would think you could use a phase-detector to compare the alternator frequency with a reference clock oscillator (50Hz or 60Hz as desired) which would give a DC correction voltage for the valve if the two frequencies are different.

The phase detector can be as simple as an XOR logic gate, or a more complex digital logic circuit such as found in a CD4046 PLL circuit.
The digital logic circuit has the advantage of generating the proper output from a zero frequency startup for the alternator, whereas an XOR only gives the proper output when the reference and alternator frequency are close (the pull-in range).

Such a feedback circuit requires loop compensation, of course, so the frequency output remains stable. A simple low-pass filter may be sufficient or else a more complex PID scheme would be required.

7. ### Mike Webb Thread Starter New Member

Mar 4, 2016
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0
The alternator is driven by a hydraulic motor as for the comments regarding a mechanical flow control device, this works fine on a fixed displacement pump, however with a variable displacement pump it is more complex. The proportional valve needs a dc signal voltage.

the vast majority of hydraulic generators I have to install are integrated into existing hydraulic circuits therefore I have to work with whatever system already exists. This particular application is to be driven from a vehicle gearbox mounted PTO pump and operational whilst the vehicle is in transit, consequently the pump speed will vary considerably and controlling this mechanically is almost impossible with any accuracy, so if I can signal the proportional valve based on the output frequency from the generator to only open the swash plate to deliver the precise flow required then I have a far more efficient system without huge issues with excess oil, heat and losses.

8. ### Alec_t AAC Fanatic!

Sep 17, 2013
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Can you post a link to the valve spec?

9. ### shortbus AAC Fanatic!

Sep 30, 2009
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This information wasn't included in the original post.

10. ### GetDeviceInfo Senior Member

Jun 7, 2009
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Pumps are typically pressure compensated, or will have that as an option. From there you add a flow control valve. What pump controls are currently employed