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September 25, 2012
What is cross-over? What causes it, and how do you fix it?
And no, we don’t mean a 4 wheel drive vehicle that combines the features of a sedan, wagon, and SUV.
As we discussed way back in Practice Tips #3 Dental Pneumatics, most dental units run on air and require air for just about everything, including turning on the water (which is “air activated”). This means there are valves inside the unit which have both air and water flowing to (and possibly through) them. A failure in one of these valves can lead to cross-over, getting the air in the water line or water in the air line.
The first step is to verify that cross-over is actually occurring. If you have water in the air line, start by checking at the compressor. Do you have good dry air coming out of the compressor? If the air is moist right at the compressor, the problem is at the compressor itself and you don’t have cross-over. Check the filters, dryer, and drain the tank. If the problem persists, additional trouble-shooting of your compressor may be required, call and speak with one of our technicians.
If the air is dry at the compressor, then you probably have cross-over, so now you need to figure out where it’s happening.
Are you experiencing cross-over in just one room or several? If it’s in just one room, that will narrow things down considerably; if it’s in more than one, you could have multiple failures, or you could have water or air working its way through the lines from one room to the others. Either way, we’ll next want to check within one room that’s affected.
Are you getting cross-over in the air/water syringe? The syringe air and water doesn’t typically go through many valves, so if you’ve got cross-over here, it’s likely from a failure within the syringe itself, or in the master valves (see Practice Tips #23 ”Getting to Know Your Utility Center”).
If cross over is occurring in the syringe itself, the cross-over could be isolated to the syringe. Check for cross-over elsewhere. Do you have trouble with the handpiece drive air? If you've got water in the drive air, youll often notice that water drips out the bottom of the unit when you use your handpiece (as the drive air typically exhausts into the unit). Do you have an assistants side syringe as well? Is it affected? If you dont have cross-over anywhere but in one syringe, then the cross-over is quite possibly within that syringe.
If it’s just one syringe, the most likely culprit is the small internal o’ring, our part #01-06. If this o’ring is missing or damaged, you can get cross-over in your syringe.
If the water just fails to shut off, you’ve probably got a worn button or valve core. Check our previous issues on syringe repair and syringe troubleshooting for more information on resolving these issues.
Another possible point of cross-over in the syringe is unique to certain brands of autoclavable syringe (such as A-dec). With these syringes, a manifold is inside the handle and the syringe head attaches to this manifold and is secured in place when the handle is threaded on. The manifold has two male connectors that are off-center and which correspond to two holes on the bottom of the syringe. One port is for air, the other for water. These ports are off-center so they will only connect to the syringe if properly aligned. In theory, this will prevent cross-over, however in reality it can cause it. If the ports are not properly aligned, the handle can still screw onto the head of the syringe, but the air and water will just flow into the cavity between the manifold and the syringe head. This creates a constant mix in the syringe handle which will yield cross over in the syringe. Ironically, even though this occurs at the syringe, this particular source can lead to air or water flowing back down the lines and yielding cross over in other items in the operatory as well. If you are getting cross over and have autoclavable syringes, always make certain that the syringe head is securely attached to the manifold before proceeding with other checks (if for no other reason, this is a very quick and simple thing to check).
This photo shows an A-dec syringe handle with the manifold.
If the syringe checks out, then we need to check other possible sources of cross over.
Every air activated valve in the unit is a potential source of cross-over, and all of them should be checked.
As mentioned previously, if you’re getting cross-over in the syringe, you could also have a failure in your master valve. The master valve is one of the most common sources of cross-over we encounter. There is a diaphragm on the master valves that corresponds to the air activation. Usually the diaphragm is under a square cover on the valve. This will also be where an air line attaches to the valve.
A few common designs of master valve are shown below with the location of the diaphragm pointed out:
Note the square covers held on with screws at the corners in the second and third photos. This type of design is very common on master valves. Look for a square cover on your master to find the diaphragm.
The third photo is of an A-dec water master. Note the yellow tubing with a red dash. This is the A-dec color-code for an air activation line (air out from the master switch on the front of the unit). The diaphragm will usually be near where this line attaches (another thing to look for to correctly identify where your diaphragm is). American Dental Accessories, Inc. carries master valve repair kits which will allow you to replace the diaphragm. In addition, the repair kits include o’rings, valve stems and springs. We recommend replacing all of these components if you’re accessing the valve interior. You can also see a manual shut-off in the third photo. The master valve normally attaches directly to the manual shut-off. You will want to use the manual shut-offs to turn the air and water off at the unit before servicing the master valve(s).
It is also common to have a relief hole in the side of the master valve just above the diaphragm. If water is coming out of this hole, this is another indication of a ruptured diaphragm.
A worn or damaged diaphragm in the water master can also lead to getting air in your water line.
Stay tuned for Part 2 next month. Well cover more valves that could be the source of cross-over, details on how to narrow down which operatory might be the source of cross-over, and the effects of air in the water line. All of this and more, next month!
February 28, 2012
Air/water syringes are the workhorses of the operatory but can often exhibit minor malfunctions. Most difficulties you encounter with your syringe can be easily addressed in just a few minutes by the office staff.
Air mixing with water (or water mixing with air).
If either button is sticking, that could cause the air or water to continue running and lead to this problem. See “sticking buttons” below. If the buttons are not sticking, the problem is likely inside the syringe head.
There is a small o’ring inside the syringe which keeps the air and water separate (the “small adaptor nut” o-ring part 01-06). This o-ring could be worn or missing and should be replaced.
It is, also, possible that there is condensation in the air line from the compressor. In this case, you would only have trouble with water mixed in when hitting the “air” button, not air mixed in when hitting the “water” button. An easy way to determine if you have water in your air line from outside the syringe is to detach the air line from the bottom of the syringe and let the air from the line blow into a paper towel or onto your hand. You’ll know pretty quickly if there’s moisture in the line.
Water can also get into the air line from other valves in the unit. See some of our previous issues for more information on trouble shooting water in the air line from other sources.
No air comes out when hitting the air button. This is almost always due to an obstruction somewhere. Start by trying without a tip installed on the syringe. If you now get air, the obstruction was in the tip. Putting it in an ultrasonic cleaner for a minute or two may clear it up. Otherwise, discard it as the tip is worn out.
If you get no air without a tip either, the clog is further upstream. Remove the holding mechanism from the syringe and check for debris on the inside of the head. Usually the holding mechanism is unscrewed using a 5/32” allen (hex) wrench. Remove the button and valve core (if your syringe uses valve cores) and check for debris here as well.
Detach the tubing from the base of the syringe and verify you have air pressure in the line. If you do not have air pressure in the tubing, the clog is at a valve or junction before the syringe. Call our techs to trouble-shoot further (or see our previous issues on leaking, junction boxes, & pneumatics).
Follow the same procedure as above for no air. Additionally, if you use plastic barriers over your syringe, it is very common to get debris on the inside as staff will often poke the syringe tip through the barrier when changing tips. If the tip is poked through the barrier, every time the tip is poked through, a small piece of plastic is shoved into the syringe with it. We frequently see syringes with a huge wad of plastic built-up inside the small adaptor nut o-ring (#01-06- see above). Check carefully as this is typically clear plastic and hard to see. You should be able to remove it with a scaler or explorer. You might want to show your staff to make certain they cease using this technique.
If there is no debris evident inside the head, continue as above (under “no air”).
This is more frequently experienced with the water button than the air button. Mineral deposits from hard water, debris in the water line, or corrosion can all wear the water button and the o’rings on it. If it is sticking, remove the button and lubricate with a silicone-based lubricant. In fact, it’s a good idea to regularly lubricate your buttons as part of routine maintenance to keep them moving smoothly. We recommend once a month, but you may want to adjust the frequency depending on your conditions and experience (e.g. if you have particularly hard water, a greater frequency may be warranted).
Lubrication may be enough to restore proper function. If not, you will need to replace the button (or valve core, if your syringe uses valve cores). As a temporary fix, you can swap the air and water buttons of your syringe. This will cause the air button to stick, but this is often less problematic than having the water constantly leak.
See our previous issues on syringe repair for step-by-step instructions on removing and changing buttons.
Most syringes are designed for quick changing of the tips so the tips are just held in with o-rings. This allows the tip to be easily pulled out or pushed in- no loosening or tightening of components. Older designs used a brass or plastic syringe cone to help retain the tip, but these required use of a wrench to unscrew or tighten the holding mechanism to change tips. The cones, however, often had a slit that ran the length of the cone which would restrict lateral movement of the tip.
Newer designs that just use round o-rings do not provide the same lateral tension. You’ve got a round peg in a round hole. Tightening the holding mechanism can compress the o-rings further limiting rotation of the tip, but it’s difficult to tighten enough without preventing easy tip changes.
Most current designs use two o-rings to hold the tip; the first o-ring (closest to the tip) can be replaced with a cone to limit rotation. Not all assemblies have room for a cone here, but most should.
The DCI collar-type syringe uses ball-bearings to hold the tip in place. DCI makes a tip with extra notches on the end of the tip. These notches will fit in-between the ball bearings of their collar mechanism making it harder to spin the tip. The DCI collar has 6 ball bearings in the mechanism, some of the other brands of collar syringe use fewer ball bearings so the notches won’t limit rotation as effectively in these syringes.
Last of all, you can rely on simple physics. Rather than pushing on the side of the tip for retraction, use the hook-like end of the tip to pull. Syringe tips are designed to stay in place when pulled on with only modest force, tips are not designed to resist rotational forces.
Leaking: Air or Water Not Shutting Off
Most syringes currently on the market have a spool-type button that serves as the valve. The button itself turns the air or water on. If the water or air is staying on, typically the button has failed. If the button has failed, simply replace it. A sticking button will also lead to failure of air and water to shut-off. See above under “sticking buttons” for possible remedies.
Some (mostly older) syringes will use a valve core under the button. This is what actually turns the air and water off and on, the button simply activates the valve core. If your syringe uses valve cores, typically the valve core will need to be replaced using a valve core wrench.
Leaking: Air or Water Coming Out Somewhere Other Than the Tip
“Leaking” can also mean air or water coming out from somewhere other than where it is supposed to. Most components of the syringe are sealed with o-rings. Leakage around any of these components will usually be remedied by replacing the corresponding o-ring.
For leakage around the holding nut, replace the large skinny o-ring (#01-05) that seals it. If you have leakage out around the buttons, replace the buttons (unfortunately, o-rings are not available for most buttons, so the entire assembly should be replaced).
A note on disposable tips: Many disposable tips on the market require a special adaptor to properly fit your syringe. If not using this adaptor, many problems can be observed such as water mixing in with the air (see above), poor spray pattern, or even tip ejection (which can cause harm to patients). If your disposable tip does not have the same shape and design as a standard tip (a skinny water line protruding out the back and a groove toward the back to line up with the o’rings) it will require a special adaptor. Regardless of brand or style, it's always a good idea to give the tip a little tug after inserting to make certain that it's properly and securely seated.
However, if the tip is identical to an autoclavable tip (just made of plastic in whole or in part – such as our Smart Tips), then you probably don’t need to use an adaptor. Of course, if you use autoclavable tips you’ll avoid this issue altogether (to say nothing of reducing waste and saving money).
For step-by-step guidelines are performing the various repairs mentioned above, check out previous issues of Practice Tips:
How to Repair a Leaky Syringe- Part 1
How to Repair a Leaky Syringe- Part 2
How to Rebuild Your Air/Water Syringe- Video
December 22, 2011
Save time and money with this helpful video. It demonstrates just how easy rebuilding your air water syringe can be.
For more information on syringe repairs and troubleshooting leaking syringes please visit the following issues of Practice Tips:
How to Repair a Leaky Syringe- Part 1
How to Repair a Leaky Syringe- Part 2
Can’t see the video? You can also view this video on our blog or Youtube.
This is the last issue of Practice Tips for 2011, and we would like to thank all of our readers for your support and suggestions. We look forward to publishing a lot more helpful time & money saving articles.
Happy Holidays from American Dental Accessories!