Tech Tip: Troubleshooting Spray Foam Pressures

Equipment is the number one source of problems when spraying foam. Knowing how to spray good foam comes from training and experience: spraying at the proper temperatures and pressures, keeping the A and B sides balanced, and knowing where to look when they drift. Here is ThermoSeal's field guide to getting it right on every project.

What Pressure Should I Spray At?

ThermoSeal foams are designed to be sprayed with the A side and B side at equal pressures, at these targets:

Spraying at a minimum of 1,200 psi and the target processing temperatures is also a condition of maintaining warranty status, as stated on every ThermoSeal technical data sheet.

Where to Start Troubleshooting

When pressures are off, work through these common checkpoints:

• Gun screens
• Y-strainer screen on the machine
• Mixing chamber side ports
• Drum (transfer) pumps
• Viscosity imbalance or cold material

Quick Guide: When One Side Keeps Falling

If the A-side pressure keeps falling

There is either a blockage on the B side at the gun:

• B-side screen
• B-side mixing chamber port

Or a restriction on the A-side supply:

• Machine Y-strainer (A side)
• A-side drum pump

Less common causes: leaking A-side gun o-rings, or leaking packings on the A-side proportioning pump.

If the B-side pressure keeps falling

Reverse the checks. Look for a blockage on the A side at the gun (A-side screen, A-side mixing chamber port), or a restriction on the B-side supply (machine Y-strainer on the B side, B-side drum pump). Less common causes: leaking B-side gun o-rings or B-side pump packings.

Steady but Unequal Pressures: Viscosity Imbalance

If the pressures are slightly off but steady, and nothing is wrong with your equipment, you may have a viscosity imbalance caused by cold weather. The B-side resin is thicker than the A side, and it thickens further as it cools.

• Raise the B-side primary heater 3°F to 5°F higher than the A side.
• Warm the drums to 77°F.
• Raise the temperature gradually. The best method is to store drums in a warm space and let the surrounding air heat them slowly. Never apply direct heat to closed cell resin drums, and do not recirculate closed cell material.

For more on winter processing, see our guide to spraying foam in cold weather.

What Unbalanced Pressure Does to Your Foam

When pressures are unequal at the gun, the mix goes off ratio, and the foam shows it:

Other causes of off-ratio foam include a clogged Y-strainer or filter on one side, a proportioner that has drifted out of calibration, and a worn mix chamber or impingement tips. Off-ratio foam cannot be sprayed over. It must be removed and replaced once the problem is fixed.

The Bottom Line

Knowing how to operate and maintain your equipment helps you avoid liability and safety issues as well as callbacks. Spray at the target pressure for the product, keep the A and B sides equal, check your gauges throughout the job, and stop to find the cause the moment they drift more than 100 psi apart.

Frequently Asked Questions

What pressure should spray foam be sprayed at?

For ThermoSeal, the target processing pressure is 1,200 psi for 500 and 800 open cell, and 1,200 to 1,450 psi for HFO and 5G closed cell. The A and B sides should run at equal pressures.

Why does my A-side pressure keep dropping?

Usually because of a restriction on the B side at the gun, such as a clogged B-side screen or mixing chamber port, or a restriction on the A-side supply, such as a clogged machine Y-strainer or a problem with the A-side drum pump. Less often, leaking A-side gun o-rings or pump packings are to blame.

What does off-ratio spray foam look like?

A-side heavy foam is dark, crunchy and brittle, with a strong odor and slow cure. B-side heavy foam is soft and spongy, doesn't hold its shape, and has a sticky surface.

Can you spray over off-ratio foam?

No. Off-ratio foam must be removed and replaced. Correct the equipment problem first, confirm good foam on a test slab, then re-apply.