Hey Guys Quick question. On a Case 420 skid steer is there a control switch or valve to change from Case to Cat controls and vice versa? Thanks
No there isn't if its a series 3 420 you can change the pilot pattern back and forth by changing the pattern kit. But there is no switch that does that. The only machine that controls their pilots like that is Komatsu. There are some issues with running pilots like that in a skid steer. The E/H machines allow for easy switching of patterns but pilot does not.
Hmmm.That's weird cuz about a year ago I ran a bobcat track loader with pilot controls that had a control switch from sae to iso. This particular 420 I've got is a series 2 I believe.
The Bobcat was E/H if it had a pattern changer. Bobcat has never run pilots. The original series 400s are servo only, they are not pilots unless it is a tracked machine made starting in the last half of 06 give or take. I think you might be confused on what pilot controls are as opposed to E/H or Servo. If you are, I can explain it.
Yeah your right I'm probably confusing the two since I'm not sure of the difference.
that is an interesting feature komatsu has... why has it been problematic??
im going to take a whack at explaining the difference bw pilot and eh. so your standard skid steer (a lot of manufacturers) has direct linkage from your hydro swash plate to your hands. this is responsive and gives you feedback but is higher effort. other skids have servo controls, which is direct linkage to a small piston which mechanically (through hydraulic oil) assists your movement of the swashplate. you have one circuit of oil between you and your swash plate. it seems that both pilots and eh have this servo control circuit as a base to their control system. with pilot controls there is another circuit of oil which helps you manipulate the piston connected to the swash plate. there is no mechanical linkage. with electric controls there are electric actuators that manipulate the piston. do i have it right?
On the Komatsu: Because it forces all flows and pressures to be the same to allow you to go from ISO to CASE controls. They don't perform well like that.
The commonly accepted definition of pilot control is a hydraulic over hydraulic system. In truth a pilot system is any type of devices that will act as an interface between the operator and the valve body other than direct mechanical actuation (like rods, linkages, and cables). Hydraulic over hydraulic: The machine will be equiped with a seperate hydraulic circuit that only serves to apply the force you are putting on the control levers to the hydraulic valve that you are trying to operate. Each of the main circuit valves will have small hydraulic pistons. These pistons are connected to the spool valve (the componenet that is inside the valve that directs the oil flow through the valve). When you activate the control lever the pilot system will manipulate the spool valve. This will direct oil through the valve which in turn will direct oil to what ever cylinder you are trying to operate. E/H= electric over hydraulic: Also known as "fly by wire". This type of system relies on variable electric current to manipulate the hydraulic valves. The control lever is a type of reostat. The proportioning comes from the change in voltage generated at the controls. Typically the more you push the lever the more voltage is sent. At the hydraulic valve you will find electronic solenoids. These are used to manipulate the spool valve (in the same manner as the piston in the pilot control system). The solenoid will react to the changing voltage. The farther you push the lever, the more voltage is sent. The higher the voltage the farther the solenoid will move the spool valve. The farther the spool valve is opened the more oil is allowed to pass on the the cylinder. Things go in reverse as you let off of the lever. As a general rule (and in my experience) the hydraulic pilot control system will offer better feed back (between the two), and the E/H can feel vague in comparison. On Edit: I forgot to mention. It is easiest, and cheaper, to change patterns on an E/H system. Usually a switch is all that is required to change which solenoid will recieve which signal. An H/H system will require a pattern changer in the pilot system. This usually requires the removal of a set screw, and manually moving a valve lever to a different position. This will change the routing of the hydraulic oil. I find it interesting to note that my Bobcat skid steer (A300) has an electronic switch that changes it from skid function to steer function, and vice versa. The other selectable joystick machines, found on Bobcats, have an electronic switch also. The pattern selector on my Bobcat mini excavator is a hydraulic pattern changer despite the fact that it is equipped with E/H the same as the skid steers.
so both systems use the servo as their foundation? i would like to see how a pilot system works and all the components involved.