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Home | Closed-Cell Foam | Ask The Expert: Flushing Equipment
flushing foam from equipment will save your job

Ask The Expert: Flushing Equipment

By Mason Knowles

Question: Should I flush my equipment when switching from open- to closed-cell? How about when switching from one brand of foam to another of the same generic type?

Answer: Foam equipment typically requires flushing when switching from open- to closed-cell foam and vice versa. There are vast differences in formulations of open- and closed-cell foam and mixing the two formulas can cause a reaction that would cause problems. Therefore, I recommend that a contractor have a dedicated foam proportioner for open- and closed-cell foam, if they frequently use both materials.

When switching between brands of the same generic type of foam, there may or may not be a reaction when the two different liquids combine. So, the answer is yes or no. A simple way to determine this is to take a small amount of the liquid material (one cup is sufficient) of both liquids and mix them together in a clean, dry container.

Check for a reaction such as coagulated liquid, development of particles, or increased viscosity. If there is no reaction, then the equipment would not require flushing before the new foam is introduced into the machine.

There is more likely to be a reaction when switching between open- and closed-cell foam than switching brands of closed-cell foam. Even if there is no reaction, care should be taken not to spray a mixture of the different foam systems when following one material with another. The resulting foam can end up being a hybrid that does not have the desired physical properties of either. Worse yet, the applicator can increase his liability since the resulting foam is neither company A or company B’s foam but a foam he created.

The following procedure can be used to minimize the potential for spraying hybrid foam:

  1. Before inserting a transfer pump into the new drum, clean it thoroughly – removing any trace of old material.
  2. Pump out the old material into a clean bucket until the new liquid is completely in the hoses. This can take two gallons or more depending on the length and size of the hoses. Most of the material can be reused and dumped back into the original foam drum. But there will be about a ½ gallon of liquid that is a combination of the old material and the new. This material should not be reused. Mix the B-side with the A- side to make foam and dispose in accordance with local, state, and federal regulations. Note: Check the internal temperature of the foam to prevent auto-ignition when hand mixing large quantities of A and B side materials. Break up any foam whose temperature exceeds 250°F.
  3. Spray samples of the new foam onto a clean, dry surface to verify that the new foam has the desired physical properties.
When switching from open- to closed-cell, be sure that you not only flush your lines, but also clean your gun.

When switching from open- to closed-cell, be sure that you not only flush your lines, but also clean your gun.

Question: How do I flush the equipment?

Answer: Ask your foam manufacturer for instructions on how to properly flush your equipment, as well as what materials they recommend for the job.

A common procedure is as follows:

  1. Flush the proportioner with a liquid that doesn’t react with the foam chemical and then follow it with a liquid that reduces the risk of moisture contamination such as DOP (dioctyl phosphate) or TCP (tricresyl phosphate). Note: DOP and TCP can be left in the equipment for long-term shutdowns.
  2. Dispose of the flush liquids in accordance with local, state, and federal regulations. •

With more than 45 years of experience as a contractor, material supplier/manufacturer, equipment manufacturer, and trade association professional, Mason Knowles has unique qualifications and a wide base of knowledge in the spray polyurethane foam industry. His positions include: Chair: ASTM Subcommittee on SPF Roofing; Chair: ASTM Specification on SPF; SPFA accredited roofing & building envelope inspector; SPFA Certified Field Examiner; Chair: SPFA Consultant Committee; Member: RICOWI Hurricane & Hail Investigation Team; Former Executive Director: SPFA; and Former Technical Director: American Plastics Council. 

Photos courtesy of SWD and PMC