Creating a Leak-Free Seal With Poly Processing Tank Fittings


We discuss a few of our popular fittings and how they are sealed to bring a consistent level of safety and environmental care to each Poly Processing tank we assemble. 

With more than 40 years of chemical storage experience, we understand the importance of using the right storage components for your application. We’ve learned how our most-regularly stored chemicals, like sulfuric acid, sodium hypochlorite, and hydrochloric acid, react to improper storage systems.

An integral part of any safe chemical storage system is the gasket. A gasket seals with a particular fitting to prevent leaks or spills. It is crucial that the gaskets and bolts used on your storage tanks are protected from corrosion caused by reactive chemicals.

Let's look at three common fitting types used in our chemical storage tanks and how they work.

Fittings Molded Into The Tank

Poly Processing’s proprietary Integrally Molded Flanged Outlet (IMFO) is molded while the tank is processing, making it a stress-free part of the tank. The flange is created from the same material as the tank – it’s not an insert introduced during or post-production.

The biggest benefit of the IMFO tank is that there is no weak point in the fitting as it is molded to the tank rather than added later. So how does it seal?

The flange itself is faced off or surfaced at the factory so that it is smooth. To seal the fitting, a gasket is placed on the face of the IMFO with the flange against it and the two are bolted together as one assembly.

This configuration has been carefully engineered to minimize the risk of leaks or spills from the day the tank is built. One big benefit for this configuration is the entire assembly is external and not bolted through the tank wall. 

BOSS_Fitting_Installed.jpgBolted One-Piece Sure Seal Fittings

Our B.O.S.S. fitting, or Bolted One-Piece Sure-Seal, is a one-piece fitting designed to reduce the seal point to a single gasket. This gives end users a robust sidewall fitting that is compatible with all chemicals stored in cross-linked polyethylene tanks (XLPE).

Here, the gaskets are on the inside of the tank. The fitting extends from the inside of the tank. Holes for both the bolts and the fitting are cut into the tank wall. An installer places a gasket on the B.O.S.S fitting that goes from the inside to the outside. A compression plate with washers and nuts is then placed on the outside of the tank and torqued down.

This allows the plate to press against the tank, pulling the gasket from the inside and sealing the surface. This process ensures a total seal.

Bulkhead Fittings

An economical option best used on small tanks or specific applications are the plastic bulkhead fittings, which are available in PVC, CPVC, and Polypropylene.

Bulkhead-683334-edited.jpgSimilar to the B.O.S.S. fitting, the bulkhead fittings seal by drilling a single hole into the sidewall of the tank. The installer places a ring gasket onto the bulkhead fitting and it goes from the inside of the tank to the outside through the hole. A compression nut then threads onto the bulkhead fitting, is tightened up and is sealed.

Of note: Because of the lack of torque value on most plastic fittings, this type of fitting is limited. It's used on smaller tanks and also for overflow on tanks 3,000 gallons or larger.

Besides PVC, another type of bulkhead fitting is stainless steel. These do have bolts that share a common stainless steel plate inside the tank. Here, there is a single gasket that goes on the fitting. To seal it, you drill the bolt and fitting holes, and the stainless steel bulkhead with the gasket comes from inside the tank out with a compression plate bolted down on the outside. This is by far one of the strongest fitting choices but stainless steel isn’t compatible with certain chemicals.

Flange-287530-edited.jpgLastly, there's a bolted flange bulkhead fitting which is a little more complex. Similar to the IMFO fitting, the gasket goes on the outside with the PVC flange. On the inside of the tank, it is married to bolts with welded washers and encased in plastic. These bolts come through the tank and have their own smaller gaskets to seal the bolt holes. In the end, the bolt holes seal from the inside and the actual fitting seals from the outside.

Need Help Choosing a Tank Fitting?

When you are sealing the fittings on your storage tank, Poly Processing is always here to help you ensure its safety and security. For more information on fittings and how they seal, contact a chemical storage tank system expert today.

To ensure all fittings are properly installed to be leak-free, view our Installation Guide.

Installation and Operation Guide


Topics: Fittings and Accessories