Practice Tips #51: Cross-Over Part 2

Last month in Practice Tips we discussed a few possible sources of cross over and how to determine if you actually have cross over. We finished up by looking at master valves.

What if you’ve got cross over in more than one room? Is it possible that one room is affecting the others? Yes, cross over can work through the lines from one room to the entire office. In fact, you can even get air in your pipes (if you’ve got air in the water line) so pipes will rattle, squeak, or groan when any source of water is used (such as a faucet or even a toilet). Of course, you can also get failed valves in multiple rooms at once.

How do you determine which room is to blame, or even tell if it’s one or more?

Since we left off last month in the junction box, let’s continue there.

In addition to your master valves, you should also have manual shut offs in your junction box. Normally, the master valves are attached directly to the manual shut-offs. The manual shut-offs have a knob that you can turn to physically stop the flow of air and water. Use them to shut both air and water off in an affected room. Start in the room closest to the compressor.

A Typical Manual Shut-off valve

Once the manual shut-offs are closed, depress the buttons on your air/water syringe until all flow ceases. Next turn the AIR manual valve back on, but LEAVE THE WATER OFF. Put your syringe tip into a cup of water and hit the WATER button of the syringe. If you have bubbles, you have cross over in that room. If you had been experiencing water in the air line, you’ll want to hold the syringe button down for at least one full minute as it may take some time for the air to work its way through the lines. If you don’t have bubbles, that room is probably fine. Turn both air and water off with the manual shut-offs and proceed to the next room and repeat this test. It’s important that you turn both valves off before checking the next room to keep any cross-over that might be occurring in this room from affecting others.

Where else can you get cross over? Any other air-activated water valve in the unit.

If you have cuspidors with timers for the bowl rinse or cup filler functions, the timers are air activated and could be a source of cross over. As cuspidors typically have large lines attached, these can affect the whole office more readily. If you’ve got squeaking pipes, your cuspidor may be a more likely culprit.

Just like master valves, timer valves can vary in design but will be mounted inside some sort of “box” or “utility center” directly below the cuspidor. The timers often have a similar appearance to master valves and will have some sort of knob to adjust the timing.

The arrow indicates one of the timer valves on this cuspidor manifold. Note the square portion of the valve with a metal cover, just as we saw last month on the master valves. This manifold also has on/off valves at each end which could have failed as well.

Other possible sources of cross over are the water relay valve or even the handpiece block.

Normally, a failure in the water relay valve will result in trouble with handpiece water long before you experience cross over, so this is not very likely unless you’ve also had trouble with your handpiece water coolant (dripping, coming out of the wrong handpiece, or other issues). Depending on the design of valve, usually the water relay just needs to be replaced as most are not readily serviceable.

Last of all is the handpiece block. There are many designs of block, so this can be more difficult to check, but often a diaphragm will be readily apparent when you inspect the block (such as in the block pictured below, as used in a Beaverstate delivery system). You can clearly see the seam between the two layers of brass in the photo. This is where the diaphragm is.

A Beaverstate style handpiece block

In many models of units, water does not actually enter the handpiece block, so you would not get cross over here. Always be sure to verify the configuration of your unit before checking the block.

If you have quick disconnect handpieces, you can also get cross over in the coupler. Normally cross over here would only be seen in the handpieces. In this case, you may see water dripping out of the unit. This is actually from water coming out the exhaust line (which often empties into the unit). If you see water dripping out of the unit (or it’s getting into your turbines) change the o’rings on your quick disconnect.

As you can see, there are a number of possible sources of cross-over in the dental office. To help you diagnose, we’ve provided a handy checklist below:

Possible Sources of Cross-over

  • Compressor
  • Air/water syringe
  • Master Valves
  • Cuspidor timer blocks (if present)
  • Handpiece block
  • Handpiece coupler (if a quick disconnect)
  • Any other air activated valves (e.g. water relay)

As mentioned above, check one room at a time to verify where cross-over is occurring then check the valves within each room to determine the precise source.


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