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 the air or water button is sticking, that could cause the air or water to continue running and lead to this problem. Syringe repair kits are available to rebuild your syringe completely as well. 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 keeping 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 an air/water syringe 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. 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 ( item number 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 (Item number 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 you're 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
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