Does Off Pressure = Off Ratio?
Short answer: Not always, but it’s one of the biggest clues you have.
When Pressures Drift, Problems Follow
When pressures drift apart, ratio problems often follow. When pressures mirror each other, ratio, density, quality, and spray pattern usually fall into place. Pressure isn’t the only indicator, but it’s often the first one to pay attention to, and the one that points to where to look next. At IDI, when frustrated sprayers call in for help, one of the first things our team asks for is a video of the glass gauges.
Why start there? The gauges provide one of the quickest views inside the system and can reveal a lot in just a few seconds.
The Quick Questions That Narrow It Down
From there, IDI can move to the next set of questions, such as:
• Where are the A and B temperatures?
• What does the spray pattern look like?
• How fast is the foam wet time?
• Is the density consistent?
• What product are you spraying, and when did things start feeling off?
What Happens When Pressures Are Balanced
The goal is to get the A-side and B-side pressures as close together as possible. When temperatures are set correctly and both chemicals are flowing well, several things tend to fall into place:
• The foam lays down smoothly without streaks or off-color spots.
• The spray pattern stays full and even.
• The density stays where it should be.
• The wet-out time feels right.
Finding the “sweet spot,” in most cases, happens when pressures are closest and the ratio is good. So, the next question is: can glass gauges be relied on alone?
Not entirely. Gauges can stick, chemicals change with temperature, and different products have different viscosities. Even so, gauges remain one of the most valuable early indicators available. They’re often the first clues that something is drifting out of balance long before the foam shows obvious signs of trouble.
How to Bring Pressures Back Together
The big lesson here is: how do A-side and B-side pressures get balanced? If the machine has AVC (Automatic Viscosity Control), Ratio Control, or Ratio Assurance, those features are designed to help stay on-ratio. However, many sprayers use reactors that don’t include these systems. In those cases, balancing pressure typically comes down to adjusting the A- and B-side primary heaters and hose temperature.
Temperature Guidelines to Keep in Mind
As general guidelines, the A-side typically runs at the lowest temperature because it’s thinner, while the B-side is thicker and usually needs the highest temperature. Hose heat should normally sit somewhere between the two, because its primary purpose is to maintain the set temperatures—not raise them.
Whatever adjustments are made, don’t go crazy. Small changes like 1 to 2 degrees with the newer HFO systems can make a meaningful difference in viscosity, pressure, and ultimately how the foam processes. The gauges don’t have to read the exact same number. The goal is to get them close enough for proper blending inside the gun, so the foam performs the way the manufacturer intended.
Don't Skip This: Confirm With Density Tests
One final thought: even if foam looks great, that doesn’t guarantee it’s on-ratio. With closed-cell foams, daily density tests are the only reliable way to confirm processing is accurate.
As with all chemicals, for specific information about the formula being sprayed, be sure to reference the safety and technical data sheets. For any of the foams IDI sells, our team can help provide these. And if there are questions on foam or any of the products IDI carries, reach out to an IDI local branch.
IDI Resources
Looking for more hands-on help with ratio, pressure, and pattern troubleshooting? Explore IDI’s upcoming spray foam trainings.
https://www.idi-insulation.com/training
Happy spraying!