In the automation world we hear words like, Solenoid Valves, Proportional Valves, Staged Valves, Servo Valves, Valve Offsets, Gains, Linear control, Non-linearized (stepped) control curves, and on and on and on.

What in the world is your sales person trying to say here? In this article I’ll do my best to explain valve types and adjustability’s. The most important piece of information I want you to understand is that material moisture, density & weight all play a role when we are trying to control the cutting edge of any piece of earthmoving equipment. And of course rubber tires do deflect while tracked machines vibrate at differing frequencies, at varying machine speeds and varying material conditions. Note: if you’d like to stop reading at this point, I fully understand!!!

Why do I feel that you the reader needs to fully understand this lesson? I’m teaching this so you will make fewer passes, accurately control the material, improve your finish grade quality, control your site tolerances to the hundredth and pass profile-o-graph requirements. Think about it from this point of view: We hear the phase “grade-control”, but in all reality we control the deviation from grade. Get it? When the on-grade light illuminates the hydraulic valve is off or in the null position. Right? So if you are trying to control grade to the hundredth someone within your organization needs to fully understand how to tune the control system. Do you really think an out of the box system is correctly tuned for your machine and the type of material you are currently working? NOT!!! If you are working a 95% compacted sub-grade material the hydraulic valve must respond with a resounding “now attitude”. The next day when you are placing rock you will need to make an adjustment to the valve or your veins in your neck will explode. The system will be so fast that you’ll end up turning it off and you’ll say something along the lines of: “It works great in the dirt, but I finish by hand.” I hear all kind of things like: “It works well in first gear, but second gear is out of the question.” These phases only confirm one thing and that is the lack of training. If your operators know how to correctly tune a control system to mimic the way they run their machine you’ll experience the ability to control finish grade to the hundredth. If not, you’ll control grade within the site tolerances and end up making several passes to achieve that goal. I’ll share one of my favorites “This system was fantastic when it was new, but it seems to be running slower with every passing year.”

First off let’s clarify the controlling devices here. All automation valves are electric over hydraulic. This means an electric signal is sent to the valve and the valve responds accordingly. This is true with the most modern systems that electrically control the equipment manufacture’s hydraulic valves. All current systems on the market are electric over hydraulic. So, we have an electric signal controlling a mechanical hydraulic valve. If you’ll think about it, we can troubleshoot a non-active valve fairly quick. The first question is: do we have an electric signal at the valve? Next, is the spool stuck due to contamination?

Solenoid Valves:
Solenoid valves are better known as the bang-bang valve, due to its on/off nature. This valve is either open or closed due to the cut of the hydraulic spool. The hydraulic spool is cut so the oil immediately flows when the spool is moved to the open position. The volume of the oil is controlled by a mechanical flow controller, which is only limiting the orifice size.

Proportional Valves:
Proportional valves are the most popular valve on the market due to their ability to “feather” action the hydraulic cylinder. The spool in these valves has an angular cut usually between 26°-37°. This means as the spool is drawn via an electric magnet the orifice is slowly opened. Many manufactures use this type of valve.

Staged Valves:
Staged valves work similar to a solenoid valve with differing spool sizes in each stage. In the past, I’ve experienced three stages and each was factory set in both the raise and lower settings for a total of 6 settings per side (left & right). The “staged” theory is; stage two over laps the end of stage one, for a short time frame two of the three valves are open and the same for stage two to three. I can not say I’m a fan of this valve.

Servo Valves:
Servo valves are the most controllable valve I know of. However, they are very susceptible to contamination. Some trimmer & milling equipment manufactures filter the hydraulic oil down to 5 microns. For clarity human blood is 10 microns! Servo valves must have extremely clean oil which is why most equipment manufactures shy away from their use.

Valve Offsets:
Valve offsets are a method of controlling the orifice opening. This is a setting that must be preformed on each and every machine once the installation is complete. Don’t be fooled here, the valve offset numeric value will not be the same for the raise and lower, as well as for each side both left and right. When I see these numeric values all set at 150, I immediately know that someone doesn’t understand what a valve offset is. Setting the valve offsets is the method used to balance the hydraulic performance of each lift cylinder, both raise and lower, and left and right.

Master this one!

Gains:
Gain settings are used to speed up or slow down a balanced system. If you’re cutting that 95% compacted sub-grade you’ll need to speed up the gains to achieve that “RIGHT NOW” attitude and then slow the response down when placing rock. Learning to adjust the “Gain” values is a must to master machine control.

Linear Control:
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Linear control uses a 1=1 signal to the hydraulic valve, while an adjustable proportional control uses the values you assign. The chart below shows the straight lined control method compared to the adjustable proportional control. Both control methods increase the electric signal the further away from grade; the greater the electrical signal, the quicker the correction.

When you think about the controlling system, analyze the number of up corrections VS the number of down corrections. All control systems will cut grade, it’s up to you to either speed up the hydraulics and shorten the wave or slow down the hydraulics and lengthen the wave. The choice is yours. So analyze the grade behind the machine, tune up the system and control the site tolerances to the hundredth. The graph below shows a system where the above grades are greater than the below grades, any idea which adjustment I would check first?

Sign Waves

Grade (0.00)

Bill Crumb is President of Machine Control Technologies. You can reach Bill on Linkedin.com and at This e-mail address is being protected from spam bots, you need JavaScript enabled to view it . Please visit MCT’s website: www.machinecontroltechnologyinc.com