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Tuning early model electrohydraulic control systems On machines with proportional control flow and or pressure there is a relationship between the operator controls and the hydraulic system. The most common problem seen in the field is the lack of linearity between these two controls being at minimum or maximum and the hydraulic responding accordingly.

For simplicity sake we will cover one of the work horses of the industry the “Cincinnati Milacron T-Line Toggle with a PC3 control”. This press is no longer in production due to the improvement of electrohydraulic control systems and the introduction of Milacron’s VISTA line and newer style of machines. But because of the number of them in the field and the presses that were similar to them we will cover them here.

We will cover here the pressure control. In your prints you should find a sheet detailing the pots that control the “zero” and the “gain”. These must be set before any other adjustments can be made. It is necessary to realize the zero and gain will effect the minimum and maximum of all pressure related functions that are controlled by the valve driver in question. There are however two distinct differences that need to be realized, those are “on board” or factory set adjustments and settings that are adjustable by the setup personnel which are typically Digital Thumb Wheel (DTW) and / or rotary or slide potentiometer adjustments that give a feed back signal to the controller proportional to the amount that we want the sequence to operate at. For example the high injection pressure and high injection speed are adjustable by the setup personnel. And while the low injection pressure is adjustable by setup personnel the low injection speed is not. Instead it is adjustable only on the valve driver board on a factory set adjustment since the part is by theory volumetrically filled by high injection and only packed out to obtain the correct weight or dimensional requirement by low injection (yes some machines use up to 10 states of pack and 10 states of hold pressure but these are all typically at the same volume since the part is by theory filled out). We may go further into proper part filling and or machine cycles if the readers of this article wish. Give us some feed back as to what you would like to see in future articles. Well lets push on.

With the injection screw in the forward position, the DTW settings at maximum, and a gauge monitoring the injection pressure press the injection forward switch and record the current settings of the machine. (On some machines you may have to move the high injection override switch out of the way to prevent the machine form going to low injection pre sets.) For example if you show maximum pressure at 70% of the DTW setting and anything above the 70% setting maintains the same pressure reading, and below 20% of the DTW setting you stay as low as the pressure will go you only have adjustment over a 50 point range. This means that with 2000 PSI as the nominal you will get a 40 psi differential for every click of the DTW versus an ideal setting of the zero and gain where the differential sees a 2000 PSI range over a 99 point range which equates to a 20.2 PSI per click of the DTW. It is important to record the original differential so the setup personnel can know what effect their adjustments will have on the machine.


To set the pressure valve driver that controls the injection end of the machine it is best to use the HIGH INJECTION DTW settings. Place the machine in a manual cycle.

NOTE : It is very important to follow all factory safety recommendations in operating your equipment. Protective gear when purging ect.........

With the screw bottomed out you should read maximum injection pressure on the gauge. If you don’t see the required pressure begin turning in the gain adjustment until the pressure is obtained. If you cannot obtain it you will need to determine why? For example worn pump, weak reliefs, ect.......We may cover these in later articles if needed.

If you are already at or close to the recommended setting you will need to reduce the gain until the pressure just starts to drop. Now go to the a 0 DTW setting. You should see as low a pressure as obtainable. This is often not zero but more likely 50 to 75 psi. Zero would be nice but unobtainable with many older systems. If you can get to 100 Psi at zero call it good and go on unless you absolutely have to have very low pressure on injection (below 100 psi). As you could guess if your pressure is high trim the zero pot down, If it is low trim it higher. If it is where you think it should be you still need to take it one way or another to ensure it is just starting to increase pressure as you increase milliamps to the valve itself. As an example a Vickers CGE 02 or CGE 06 is operated at maximum of 400 milliamps. It usually reaches its maximum at about 385 milliamps. Also it only starts to close the metering orifice off at about 65 or 70 milliamps. (This can be measured by taking one of the two wires going to the valve loose and putting a Digital Volt Meter or DVM in series and dialed in to read 0 to at least 400 milliamps). If you are reading say 2000 psi but your valve driver has an output of 420 milliamps you can reduce the setting of the DTW by probably 10 or 15 clicks before you will see any change in the actual pressure. If you instead you dial the gain into 385 milliamps or so at 2000 PSI you should see an immediate reduction in pressure in proportion to the amount the DTW is reduced. Hopefully it will be linear. If it is not exact do not be greatly concerned. Remember the goal is to be able to adjust the machine “some” with every click of the DTW. Of all the machines I have seen in the field very few have had much more than 80 clicks for the entire adjustment range of 2000 PSI.

When you adjust one be sure to check the other since they are almost always proportional to one another. Once you have the GAIN and ZERO set we can go on to the settings that are factory set knowing that any adjustment made by the DTWs that are controlled by the valve driver we have just tuned will have a minimum value equal to X and a maximum value equal to Z. And if we have done our job well it will be adjustable with every click of the DTWs proportional to the maximum pressure obtainable divided by the number of clicks on the DTW. For example 2000 psi divided by 99 clicks equals 20.2 psi per adjustment increment. You can now move on to the factory settings and dial them in per print. Typically you will have the following settings as a general rule of thumb. 

After finishing with the pressure you can move on to the speeds. It should be noted that the Vickers CGE has a pre filter that should be checked for cleanliness before setting the ranges.

Also the Dynex valve used for speed control on the earlier T-Lines (PJ-5000 series) has a prefilter in it by the force motor.

On a final note be sure to record all before and after settings, date, time, and technician doing the work. This extremely useful when troubleshooting in the future. Good record keeping is essential to long term preventive maintenance.