Polyvinyl Coated Ductwork (Get lab test info)
For underground Air Ducts, Fume Exhaust and Solar Systems
– Saves on Labor
– Saves on Concrete
– Saves on Time
– Saves on Space
4 x 1 PCD for underground Duct Systems
4 x 1 PCD has the 4 mils of polyvinyl coating on the outside to provide protection against corrosion from the soil.
Specified by more engineers and architects than any other underground HVAC duct system.
PCD….easy to handle, easy to install
One man can easily lift and carry a 10’ length of 20” diameter PCD around the job-site…while two men can lift and position a 20’ length of 20’ diameter duct.
The use of PCD Ductwork eliminates the need for encasing in concrete, propping up or tying down. Since only a shallow trench is required, PCD Duct will not float. Because no additional concrete is required, savings can be considerable.
By combining the strength of steel and the chemical inertness of plastic, PCD Ductwork is both lightweight and corrosion- and weather-resistant. PCD will not rust, chip, crack, peel, corrode or produce odors. Although light in weight, PCD Ductwork is strong enough to walk on and will not collapse under concrete.
How PCD is made
The PCD manufacturing process begins with (1) prime, hot-dipped, G-90 galvanized steel that is cleaned and fire-treated. Then (2) a special epoxy primer is bonded to both sides of the metal. Finally (3) a 4-mil polyvinyl coating is heat-fused to one side (4 x 1) or both sides (4 x 4).
Working with PCD
PCD is a rugged, durable material that will take ordinary handling and shipping without damage. It can be cut and formed with regular sheet metal equipment and tools with no harm to the coating. Even the largest diameter ducts are easily cut with portable metal-cutting saber saws or circular saws.
A PCD connector should always be used for connecting two sections of duct. This provides a permanently corrosion-proof joint. Use sheet metal screws every 6” around. Ends of fittings are made to slip inside duct, so where a fitting is used a connector is not needed. All PCD fittings are accurately sized and fabricated with stainless steel fasteners.
All joints should be wrapped to prevent air leakage and to keep dirt and sand out of the duct system. PCD Tape is recommended as it is ideal for this usage. It has superior adhesive qualities, even in extremely hot or extremely cold weather.
Also available, as an insurance factor, is PCD Duct Sealer No. 8—a flexible and self-curing air pressure sealant. This can be applied from one-gallon cans by brush application. It provides a positive sealing of joints and screw holes. PCD Duct Sealer No. 8 may also be obtained in a cartridge package. Approx. coverage is 375 lin. Ft. per gal. @ ¼” bead.
Hardcast Tape is an alternate method of sealing joints. Hardcast Tape is a mineral impregnated cloth which must be wet with an “activator” sealant before applying. Usage is approximately one roll of Tape (3” x 300ft.) to one gallon of Sealant.
If, through a field accident, the PCD coating is scratched or scarred so as to expose the base metal, apply PCD coating compound. This is sprayed on via an aerosol can. PCD Tape can be used to cover minor scratches.
PCD Installation Guide – Underground Ducts
Install Above Water Table The PCD duct system is not designed to be waterproof. Installation must be made safely above the water table. Ducts should not be placed where water infiltration may occur.
The top of the duct can extend into the cement, leaving a minimum of 2 ½” of cement above the top, or the duct can be placed well below the cement. However, the duct should not be placed so deep that the weight on it will exceed the load capabilities.
Trenching and Backfill
After the excavation has been made, no special bedding need be used for PCD Duct. It can rest right on the ground, or be set in sand or light aggregate. Pea gravel or sand (or the material taken from the trench, if equivalent) can be used to backfill. Spread the backfill material evenly around the duct making sure there are no gaps, and tamping in place is a recommended practice. No cement is needed to fill in around the duct, since the tamped fill holds the duct in place and the plastic coating prevents ground corrosion of the galvanized steel. This plastic coating is resistant to any minerals or salts that may be in the backfill soil. PCD Duct will not “float” when backfilled to within 2” of the top of the duct. Concrete is then poured so that all “tie-down” work is eliminated.
CAUTION: When backfilling or grading, care should be taken not to dump or push heavy loads directly on the duct, nor should heavy equipment be allowed to run over the duct. It can be crushed under thoughtless abuse.
Large Diameter Ducts
Special care should be taken with large diameter ducts. Backfilling and tamping should be done without damage to the ducts. Temporary bracing can be used inside the ducts or angle rings can be permanently installed on the ducts to provide strength and rigidity. Rings should be primed and coated with PCD paint.
Polyvinyl Coated Ductwork Load Specifications
#1 Standard 4” – 8” 400 lbs./Linear Ft. 10” – 12” 600 lbs./Linear Ft.
#2 Corrugated 14” – 36” 1800lbs./Linear Ft.
*All ducts 14” or more in diameter are corrugated for extra strength.
Where deeper burial or heavier loading is required duct gauges can be increased. Also angle rings and/or special bracing can be used.
Polyvinyl Coated Ductwork Durability
PCD needs no protection in earth from sand, concrete or plaster. It is not affected by the minerals and salts found in normal backfilling materials. PCD has also passed thousands of hours of accelerated salt spray, humidity cabinet, and water immersion tests with no loss of adhesion or corrosion resistance.
Specifications for PCD Underground Air Ducts
Underground duct systems shall be PCD as made by Foremost Manufacturing Company, Southfield, Michigan.
All ducts shall be PCD formed into spiral tubes. All couplings and fittings shall be factory fabricated of PCD. All joints and connections shall be screw fastened and taped in accordance with manufacturer’s recommendations to assure an air-tight system. Any damage to the coating shall be repaired with PCD touch-up paint or PCD aerosol spray.
All ducts and fittings shall be installed and back-filled according to manufacturer’s recommendations, using pea gravel, sand or equivalent with good compaction.
Polyvinyl Coated Ductwork Fume Exhaust Systems
Rectangular Duct Systems
Spiral Pipe Systems
PCD is an ideal material for many fume exhaust applications. Combining the strength of steel with the chemical inertness of plastic PCD offers completely integrated systems with diameters from 4” to 60” spiral pipe and all standard and special fittings that may be required. The assembly of the system is completed by the use of PCD No. 8 duct sealer and PCD tape or Hardcast tape.
Two Types Available
Polyvinyl Coated Ductwork for fume exhaust is available in two styles, 4×4 and 4×1 REVERSE.
4×4 has a 4 mil coating of polyvinyl chloride on both sides. It gives maximum interior and exterior protection.
4×1 REVERSE, a more economical system, has the 4 mil coating on the inside and a grey wash coat on the outside for jobs where extra protection is not needed for the outside of the duct system.
Flat Sheets Available
Also available in gauges from 26. ga. to 18 ga. are flat sheets or wide coils for making hoods or forming rectangular duct systems.
Practical usage range is from -30º to 200º F.
PCD has been used with great success for many major exhaust systems. However, it is up to the user to determine the suitability of PCD for any particular job. Samples will be provided upon request.
Specifications for Fume Exhaust Duct Systems
Fume exhaust system shall be PCD type (1) manufactured by Foremost Manufacturing Company, Southfield, Michigan. Gauges shall be standard SMACNA gauges for low pressure systems.
Round ducts shall be roll-formed spiral pipes. Fittings shall be factory fabricated with stainless steel rivets. All fitting seams shall be caulked on the inside with PCD No. 8 duct sealer.
All connecting joints are slip-fit. Apply No. 8 sealer to all raw edges and male ends. Secure joint connection by installing sheet metal screws with a minimum spacing around 6”. Apply No. 8 sealer over screws and seam of joint and wrap with tape (2).
Repair any damage to the coating with PCD touch-up paitn or PCD aerosol spray.
(1) Specify 4×4 or 4×1 reverse.
(2) Specify PCD tape or Hardcast tape.