Sumitomo Sh120-2 Proportional Solenoid

[Huffa]

Our SH120 keeps cooking it proportional control solenoid/valve. I thought it was being caused by some frayed wires by the plug. I repaired them and installed a new solenoid but it cooked it instantly. I checked the voltage coming out of the wires that connect to it, one had 27 volts coming thru the other nothing. I take it this is the issue, does anyone know how many volts should be going to the solenoid? Does anyone know if I can do away with the electric solenoid valve and change it to a mechanical arrangement? The pump is a KYB psv2-55t Thanks

 

[iowahill]

We have a 1990 Link Belt LS4300 built by Sumitomo that I've been slowly bringing back to life. The proportional control valve on our Uchida pump runs either under computer control OR in Bypass mode if the Bypass switch is thrown. The solenoid is a 24 volt coil that when not energized reduces the two main pump pressures to under 2000 psi at idle (at least on our machine). That 24 volts HAS TO BE FED WITH REDUCED CURRENT through a large resistor, in our case a 50 ohm 50 watt as original and under the operator panel to the right of the operator's seat.

Because we are running full time in bypass mode we energize that 24 volt coil via a switch AND THROUGH THE 50 OHM RESISTOR SHOWN IN THE WIRING DIAGRAM to provide maximum pressure (~5000 psi) all the time which is how the original Bypass mode switch works, verified by tracing the electrical schematic diagram. That 50 ohm resitor limits the amount of current that the coil draws and is EXTREMELY IMPORTANT if your machine is wired in Bypass mode without the computer!

The Proportional valve in Computer mode is controlled by current from the computer determined by comparing engine RPMs to hydraulic pressure from sensors in the high side of the control valve assembly, the idea being to increase or decrease pressure(s) according to load/RPMs.

With no current the solenoid pintle is at rest with no spring pressure against it. As it is energized by either control current from the original computer OR... the voltage and current coming through the 50 ohm resistor the solenoid pushes against the spring to open the shuttle valve to increase main pressures.

I may have this wrong and am receptive to any criticism, but I would have to assume that your machine has been bypassed like so many of these and has a direct 24 volts going to the coil, thus frying it after a brief period.

 

[iowahill]

Our SH120 keeps cooking it proportional control solenoid/valve. I thought it was being caused by some frayed wires by the plug. I repaired them and installed a new solenoid but it cooked it instantly. I checked the voltage coming out of the wires that connect to it, one had 27 volts coming thru the other nothing. I take it this is the issue, does anyone know how many volts should be going to the solenoid? Does anyone know if I can do away with the electric solenoid valve and change it to a mechanical arrangement? The pump is a KYB psv2-55t Thanks

BTW, one side of the coil wire is ground, the other is the hot side. Doesn't matter which as this is only a solenoid.

 

[Huffa]

Man thanks so much for your input, it all makes sense. Yes our machine has a bypass button beside the seat that at times when it was playing up electrically we used to press and run in bypass mode. When pressed you would hear a clonk or click and the machine would work without the ecu, performance would be slightly down. However after running it like this for extended periods bypass mode just stopped working. Press the button now and the bypass light comes on but no clonk or click and it doesn't change anything so for several years its been running with the ECU, I actually installed a new ECU not long ago to see if it was something to do with the electrical gremlins it has, but I don't think it made any difference. So with our ECU operating why would I be getting 27 volts at the plug for the solenoid?

 

[Huffa]

I tapped a hole in the bottom of a burnt out solenoid and threaded a bolt in and adjusted the plunger in the solenoid up so its pressing the pin in thinking that would swash the pump to full pressure but it had no affect, why is that?

 

[iowahill]

Man thanks so much for your input, it all makes sense. Yes our machine has a bypass button beside the seat that at times when it was playing up electrically we used to press and run in bypass mode. When pressed you would hear a clonk or click and the machine would work without the ecu, performance would be slightly down. However after running it like this for extended periods bypass mode just stopped working. Press the button now and the bypass light comes on but no clonk or click and it doesn't change anything so for several years its been running with the ECU, I actually installed a new ECU not long ago to see if it was something to do with the electrical gremlins it has, but I don't think it made any difference. So with our ECU operating why would I be getting 27 volts at the plug for the solenoid?

27 volts would be the full charge output from the alternator to the battery and might be within acceptable limits for your machine. An old or aged battery charges at a higher voltage than a new one but I don't see your 27 volts as an issue in this case.

The Bypass switch on our 1990 machine was a simple toggle switch, not a push button that likely activates a relay to effect the same thing as our older and simpler wiring does/did. But look to MAKE SURE the bypass has that current limiting resistor in series leading to the hot side of the coil. I think you'll be able to sleep better after that!

Now, on to my own issues in pulling and repairing the main pump on our own 35 ton beast due to low pilot pressure.

 

[iowahill]

I tapped a hole in the bottom of a burnt out solenoid and threaded a bolt in and adjusted the plunger in the solenoid up so its pressing the pin in thinking that would swash the pump to full pressure but it had no affect, why is that?

I don't know how your valve operates but ours is a simple straight push with O rings on the exposed portion of the valve piston. Applying power pushes the piston into the regulator housing to increase main pressures (valve #1 below). Clever "bush fix" idea on your part though!


View attachment 207941

 

[iowahill]

Man thanks so much for your input, it all makes sense. Yes our machine has a bypass button beside the seat that at times when it was playing up electrically we used to press and run in bypass mode. When pressed you would hear a clonk or click and the machine would work without the ecu, performance would be slightly down. However after running it like this for extended periods bypass mode just stopped working. Press the button now and the bypass light comes on but no clonk or click and it doesn't change anything so for several years its been running with the ECU, I actually installed a new ECU not long ago to see if it was something to do with the electrical gremlins it has, but I don't think it made any difference. So with our ECU operating why would I be getting 27 volts at the plug for the solenoid?

If I understand correctly, the 27 volts is what you should be getting for full Bypass mode. The other wire should be ground (0 volts). But if the machine had been rewired other than stock then I would guess that the current limiting resistor was left out and thus feeding raw voltage at full battery current to the solenoid coil. That voltage has to be current limited.

Please note that I can only relate to how OUR 1990 LS4300 CII operates.

 

[Huffa]

So I have a new solenoid in hard wired with resistors to provide 400 milliamps of current but it looks like I may have lost the push pin that the solenoid pintle pushes against in the pump to ramp it up. Does anyone know what that pin even looks like or if its possible it dropped out between me changing solenoids over?