In this issue, I would like to take a look at pressure imbalance issues such as an E24 indication in the Reactor® Series or analog gauges reading high or low in other proportioner platforms.
There are many causes for pressure imbalance and we need to focus our attention to the correct area to get us back up and running. I like to say there is no money in machine repair down time. So instead of a “shotgun” approach where you clean every filter, clean the gun, replace mix chambers, swap guns and feed pumps and still can’t find the root of the problem, I propose a more focused approach where we listen to what our guns and gauges are telling us.
A very good friend of mine, Craig Hier with Intech Equipment & Supply liked to call it “The Rookie Rag” approach. This is a great way to teach the concept. If we can determine which chemical – “A” or “B” – is coming out of the gun, then we can place a rag over that side’s gauge and focus on the other side where the problem lies. This will immediately save us time by focusing on the side that is lacking chemical or is the cause to our problem. That said, let’s explore some of the common causes for a pressure imbalance situation.First, we need to understand that the restriction of the mix chamber impingement port sizing creates the backpressure that we monitor at the fluid outlet gauges. Think of it as blocking the end of the garden hose. The more we block, or “restrict” the opening, the greater the backpressure we create. Most polyurethane foam chemistry requires 1:1 by volume ratio and pressures balanced within +/- 200 psi or so to give us the proper yield.(Consult with your chemical supplier for their recommendations.) Remember, we are looking for clues as to why we are lacking one chemical or the other at the gun outlet.
If we have determined the “A” (ISO) side to be lacking at the gun, then we need to check the gauge backpressure readings. When the “A” side is higher than the “B” side, this indicates a restriction on the “A” side anywhere from the gun mix chamber back to the fluid outlet manifold. In other words, we are holding our thumb over the “A” side outlet. These restrictions can include blockage in the mix chamber, gun screen, whip hose, hose temperature sensor or main fluid line. Other causes easily overlooked could include the possibility of the “A” side chemical being thicker than the “B” side which is often due to cold material, heater problems or the “B” side port having been increased by wear. In this case, we are reducing the “B” side backpressure while causing a resin-rich, or too much “B” condition.
If we stick to the same “A” example, but we find the “A” side fluid gauge to be lower than the “B” side, this indicates a problem from the fluid outlet gauge back to the drum feed supply. This results in starving the supply with one of the following scenarios: supply feed pump malfunction, restriction of the feed hose or filter strainer, drum not properly being vented due to bung in place, desiccant breather clogged, debris in the bottom of the drum container, dented drum bottom restricting the feed pump inlet, “A” side proportioner pump has debris, or a stuck ball in the inlet or discharge ball check seat area. Again, one problem area that is often overlooked when circulating material back to the drum is that the control valve could be leaking, or diverting pressure and material back to the drum.
The previous example focuses on the "A" side. However, if you have determined that the "B" side (Resin) is the cause of the pressure imbalance, apply the same tests to the "B" side.
So let’s save the “shotgun” for bird hunting, and save time and money for our business by paying attention to what our gun and gauges are telling us.
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