: Hello All,

: Has anyone else had trouble with their plunger-type epoxy pumps? I just had
: another one go bad. During the downward pump stroke, it spits a slug of
: air. There must be a bad seal or check valve that lets air in during the
: up stroke even though the pump is almost new. Is there a fix for this? For
: some reason, it is only the resin pump that I have had trouble with. I
: tried heating the resin and pump thinking that there might be some
: crystalized resin gumming things up, but it didn't help.

: Thanks,

: Jon

I find that when the resin pump has not been used for a few days, it won't burp, but as soon as I get to mixing several batches it burps. The first full gallon of resin that I used, the pump burped with almost every stroke. I got a clean container and started pumping resin into it trying to prime the pump. After pumping about half a gallon I gave up and poured what I pumped out back ino the original container. The epoxy company suggested that you pump into a marked cup to verify proper proportions.

Even though I was disatisfied with the pumps, It still beats pouring out of a container and having dribbles running down the side. Though I haven't depended on the pumps for proper ratioing due to the burp problems, I have recently checked the pump ratios and discovered the ratios are off. I Let the resin sit for several days without using it, then got a burp free full pump into a graduated cylinder. I did the same for the hardner into a seperate graduated cylinder. The ratio was hardner rich, or resin poor. The resin came up short by 1/5 of its intended volume. (Unless a 1:5 ratio means 1 part hardner out of a total of 5 parts product, which would mean 4 parts resin. If this is the case, I have built two kayaks and other misc. projects with improper ratios) I revarified the ratios out of the pumps several times and it was always 1 part hardner to 4 parts resin. I was glad that I had not depended on the pumps. When the pumps where new, the volumes of the pumps where varified using the manufacturers premarked cylinder and all was well. That was 4 gallons and 3 years ago.

Bottom line, I don't and won't trust the pumps, but think of them as a handy, drip free dispenser.

Tip on measuring/mixing cups:
Instead of marking every cup, or reusing the same cup over and over again(don't use it after a prvious batch unless you wiped it out because the epoxy in the bottom of the cup will through you next mixes ratios off), cut a window in the side of a cup. Then drop another cup inside of that. Measure out proper ratios into the inserted cup and mark the cup with the window for the height of resin and total height for resin with hardner. (I used kitchen measuring cups and spoons and measured water to set the ratios on my windowed cup) Now you can drop a new cup into your calibrated measuring device for each mix.

I have a number of different calibrated ratioing devices for mixing up different sized batches. I have small and medium dispensing cups, but most often I use plastic yougart containers, margerine tubs, or chip dip tubs. If you let the epoxy residue sit in the tub after use, the next day you can break it lose as a single unit and start with a clean cup. If you wipe it out with a paper towel, it won't be totaly smooth and clean the next time you use it and you won't be able to break out the thin film of hardend epoxy as a single unit, which leads to having little hardend flakes in you next mix...if you try to reuse the cup.

I also experimented with a homemade balance. I set the pivit point of the balance 1/6 of the way from one end. That way you get 1 part on one side to 5 parts on the other side. To my dismay it didn't work effectivly. I think the mass of the moment arm counter acted the small mass being measured on each side of the balance. I suppose I could have compensated for the arm's mass, but wasn't sure how to do that.

Well so much with all my trials and errors. My suggestion is to go with a digital balance because you can tarr (zero) the balance once you've placed an empty cup on it. Just make sure you know the proper ratios by weight as ratios of volume do not always equal the ratios by weight due to different densities of epoxy and resin.

Another suggestion is to check with any local universities or even high schools. They may have switched over to digital balances in their laboratories, and have some triple beam balances laying around destined for the recycle bin. If you make a visit in person, bring along some pictures of your project so they know you are serious about the intended use for the balance. Although measuring is not as quick as using a digital balance, you can't beat the price of a freebe.

Hope this helps.

Tom