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Practice Tips #89: How to Troubleshoot a Leaking Foot Control

In 2013, we shared how your foot control or rheostat does more than just drive your handpieces. We discussed the common internal components and how multiple tubing lines send air to activate key functions in your delivery unit. If you want a great primer on how your foot control works, we recommend starting with Practice Tips #61.

This month our focus will be on troubleshooting a leaking foot control. While it may seem an overwhelming task, the foot control is really a simple assembly that you can repair yourself. Yes, YOU CAN!

Leaking After Installation of a New Foot Control:

No matter how many tubing lines are on the foot control, one of the large tubes has a “rib” that resembles a seam. This rib runs the length of the tubing and indicates the air “in” hose to the foot control.

2-Hole-Tubing-Diagram4-Hole-Tubing-Diagram

  • If after installing a new foot control, you hear an internal air leak, more than likely you have the drive air “in” tube connected to the outlet. Simply reverse the two large lines and the problem will be taken care of.
  • If the leaking is not happening on a new installation, you will want to follow the next steps to determine where the leak is so that you can correct it.

A word of CAUTION: Be sure to turn off the unit and bleed the air before opening the foot control cover to avoid ejecting any internal components. It is imperative to wear safety glasses when doing equipment repairs.

How to Remove the Cover:

  • Turn the foot control over. You will see either four or six screws around the outer edge of the foot control - remove those screws. DO NOT remove the screws from the center. These hold the main valve cylinder block onto the foot control base.
  • Flip the foot control right side up and remove the cover along with the foot control retaining ring. It is not a bad idea to take a few pictures of the internal components and tubing hookups so that you can correctly reassemble the foot control after repairing the leak.

How to Check for Leaks:

Check the hoses, are they stiff or cracked? Is the tubing all the way on the barbs?

With two-hole tubing, it is easy enough to slide the tubing clamps back and cut a few inches off the tubing and re-attach it to the tubing barbs. Insert a flat head screw driver between the tubing clamps & foot control block & twist the screwdriver to push the sleeves back. You can then grasp and pull them off with a pliers. When you are ready to re-attach the tubing, use our sleeve tool to slide the tubing and tubing clamps back onto the barb. The process is a bit more complicated with multiple line tubings, feel free to give us a call and we can talk you through that before you pull anything apart.

As always, keep spare tubing on hand as your foot control tubing can get damaged by being stepped on or run over by a chair.

Are the tubing barbs loose?

Remove the tubing as above and carefully tighten the barbs, then re-attach the tubing. It is not a bad idea to trim the tubing back a bit, so it is securely re-installed onto the barbs.

Is the main valve cylinder block loose?

Tighten the two screws in the center of the foot control base that holds the main valve cylinder block in place. There is an o-ring that helps seal the cylinder block to the foot control base. If worn, replace this o'ring.

Leak at the stem or piston?

To test whether the leak is at the piston or stem, remove the foot control cover and large spring from underneath the cover. You will need to hold down the stem/piston with your thumb and turn the unit back on to determine where the leak is coming from. Be very careful as parts can be ejected.

PISTON TYPE: The leak will normally originate from a worn or broken poppet (see diagram below). To gain access to the poppet, remove all the loose components from the top of the foot control’s main valve cylinder. Lay the parts out in the order you removed them so that you can re-assemble the foot control correctly. Then, flip the foot control over and loosen the two screws (which we told to you leave alone earlier). Next, remove the foot control main valve cylinder block from the base. You will find another spring which holds the poppet in place. If the poppet is broken or worn - replace it. American Dental carries a full line of repair kits to work with most brands of foot controls.

Foot Control Kit Diagram

STEM TYPE: Leaks aren’t as common on this type of foot control, but you should replace any damaged or worn o-rings and be sure to check for loose or cracked tubing. Tighten the main valve cylinder block to the foot control base if it is loose.

This month’s Practice Tips has borrowed heavily from our excellent equipment repair and maintenance book/CD, “Doctor, Did You Check the Breaker, Too?” This handy resource will aide you in keeping costs and downtime to a minimum. We do not expect you or your staff to become repair technicians, but perhaps learning a bit more about your equipment will make simple repairs and maintenance less intimidating. Check it out yourself!

Find more Practice Tips like this one in our archive.

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