Windshield Repair Forum

I thought it would be best to start a new post on this one, 2hipp4u posted a question about PSI on another post. I was just talking to a friend yesterday about this I would really like to measure this myself any ideas how?
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Brian,

So far I've never heard of a way to measure pressure using a manual injector setup. I'm sure if anybody knows it would be Jeff from Delta. I did have the opportunity 2 years ago to work with a tech that used a power vaccum and pressure pump with gages. On a heated shield he never went over 25 psi to fill a bullseye. He did happen to show me what would happen at 35-40 psi. It left the imprint or daisy effect. He also stated that in the winter months that he could run up to 40 psi on a bullseye without daisying. Personally, I've been using Desertstars method of starting with the least amount of pressure and slowly working up if neccessary. Same goes with stars in the hot summer months. I always slowly increase pressure along with very light probing to get these legs filled. I guess for new techs the best advice with pressure is patience, practice and caution. Not sure if any of this info helps answer your question!

My 2 cents ....

I believe that we are actually dealing with two different pressure values:

1. The amount of pressure that the injection system uses to force resin into the damaged area.

2. The amount of pressure required to maintain an adequate seal between the injector and windshield.

IMO, it is kind of a double edged sword. While one might assume that an injector that forces resin into a damaged area at higher pressures would more rapidly/completely affect the repair, the tighter the seal has to be to avoid "blowing out" your repair resin.

Much has been discussed about "high" pressure resin injection possibly causing daisies and definately/possibly (if set too high) causing additional damage to the repair area.

As well, much has been said about the fact that the more pressure used to maintain windshield/seal integrity, the more you can restrict the flow of resin into the damage.

My math may be a bit screwy, but assuming (again) that for every action there is an equal reaction, if one was to inject resin at 90 PSI, one would have to have at least 90 PSI of seal to windshield pressure to avoid the "blow out." This would then total at least 180 PSI applied to the damage.

This is the reason why I, personally, selected Delta's "lower pressure (but progressive)" system. I believe that resin will follow the least path of resistance and that the less stress I place on a damaged area, the better chances I will have affecting a quality repair without causing further damage.

I'm sure that Delta has the data/physics very well researched and can certainly respond much more authoritatively, but why use a pile driver when a thumbtack will do?

I remember those days of which you speak, Brian. Lots of windshields were blown out using those mechanically pressurized systems.

Generally speaking, I think that ANY decent MANUAL repair injector system has the ability to provide sufficient pressure to effect a quality repair and generally speaking without the danger of too much pressure resulting in a blow-out. I'm pretty sure they just can't provide that much pressure.

I can't recall EVER blowing out a windshield even if I introduced ten drops of resin and screwed the stem completely to the bottom. Neither the plastic, aluminum or stainless steel injectors appear to have the tolerances capable of applying the amount of pressure necessary to pop the w/s.

In fact, I've found that the resin is forced back out the entrance somewhere in the screw-down process depending on the resistance of the repair area.

Therefore, it seems to me that our most concern is in the area of avoiding daisies in bullseye repairs. As we all know, a good system has the ability to generate enough pressure to accomplish that.

Ergo: that's why I apply pressure gradually while eye-balling the resin travel.

Is the question of PSI moot when using manual equipment? I'll be interested in seeing other posts on the subject. Perhaps from anyone who has split a windshield using same and what make of equipment they were using at the time.

I also wonder if an injector assembly with closer tolerances would fill long cracks quicker or would time and patience still be the determining factor when repairing those cracks?

If the former turned out to be true, I'd be inclined to purchase an injector assembly designed to be used exclusively for long cracks and nothing else.

Other thoughts?

Seems that trying to quantify "psi" is irelevant to normal manual equipment. Nobody knows what psi they are working with, and with a manual injector, there is no way of knowing during the repair.

It' an interesting topic.. I am curious how much psi the different injectors are capable of. Maybe someone can do some testing.

You would need a simple pressure gauge and fittings to drill and tap into the side of the injector bodies, or better yet, rig up a special testing jig that has the gauge hooked up to a hole which can be covered by any repair device.

I might just do that... as soon as I get my taxes done anyway... Speaking of taxes, I better go work on them now. It's April 9th today, right?

You lost a week somewhere, Glassdoctor. It'a actually April 16th.

Would be an interesting test, but as you say, probably irrelevant except for our general information unless as a check to see whether one's injection system is up to par and the injector system needs replacing because of wear.

I can see that possibility with the original Novus-type plastic stem and cylinder but not the ss or aluminum. I think some types of resin may erode the plastic over time resulting in looseness. (I'm not positive about that.)

In any event, it would be far simpler to just purchase a new injector assembly rather than investing in a pressure checker.

Anyway, I think most of us today have pretty much invested in the ss. I had a couple of aluminum when they first appeared and thought they were the cat's meow until the bridge hit the ground and the stem bent beyond further use.

Even though this didn't answer Repair1's original question, I think it bears some second or third -cousin relationship.

If you perform it, I'd be interested in the results. If I were a manufacturer, I'd SURELY be interested in the comparative results among different types of manual equipment.

At the risk of beating this topic to death within my post (there isn't going to be a test for those who have already quit reading or quit now), I find Brian's question interesting for another reason.

Whenever I've felt the need for maximum pressure, I've increased the amount of resin and screwed down on the stem as far as I can without getting any backwash. A waste of resin unless one is working fleets at the time because the excess is discarded.

But, someone correct me if I am wrong.

Don't ALL of the manufacturers who use the three piece injector assemblies incorporated into their bridge kits buy from a generic supplier?

If that's the case, we'd be comparing apples to apples, wouldn't we? What we would REALLY need to do is test various (preferably) stainless steel assembles against each other.

Someone enlighten me. Is there more than one manufacturer of those?

Theoretically, I'm betting that with REALLY close tolerances, one could, in fact, blow out a windshield using a manual system. Maybe that's the reason the stem seems so sloppy in the cyclinder.

It all boils down to the seal against the glass. It doesn't matter how much pressure the injector can generate if the seal can't hold. And this is directly related to the "screw-down" pressure against the glass. The more psi, the more pressure required to keep the seal form leaking. I'm sure some seals are better thatn others and can sustain more psi given the same force applied to hold it against the glass...

That's interesting too.....

I think the only time a ton of pressure is even good is if you are working with cold glass or very thick resin. Under normal circumstances, a simple ss injector can badly daisy most repairs as it is. Do we need more pressure?

Guess I agree.

I hadn't taken the seal out of the equation but still wondering why the loose tolerances in every injector assembly I've ever used.

Any ideas other than a slip-shod manufacturing process?

Where are you when I need you, Repair1 or have you already given up as to any definitive answer to your original question ?

Time for a brew.

I use GT's VP 5000 which has a vacuum/pressure gauge (maybe most of you know this already)

The pressure gauge goes to 100 psi, which I have never gone up to!
On a normal bulls-eye break I start with 20 psi and after a few cycles I usually end my pressure at 40-50 psi.

I have gone up to 60 psi but could see the injector o-ring start to lift up from the surface of the w/s. GT recommends not going higher than 70 psi.

This does not answer the question about what a manual injector has for pressure but may help those asking in general what the pressure is when performing a repair.

note: regarding the "daisey" effect, the only time I produced one was on a hot summer day using 60psi....hot glass and too much pressure injecting the resin.

Ok there is some confusion here. As far as the pressure against the glass from the seal that has nothing to do with your injector pressure. Your seal should be just barely touching the glass just enough to create a seal I usually get a little blowout and always will if I was to push or screw down the injector to much. This tells me that less pressure works fine.
However there are other Novus type injectors that will swell as you tighten the injector my curiosity is when that seal is swelling are you loosing pressure into the break if so how much, does it get weaker with age as they seem to swell more with age. Even the Delta seals will swell a bit with age, are we loosing pressure? I would think so I