Plumbing Pressure Problems? Come to PAPA

By Ron George, CIPE, CPD, President, Ron George Design & Consulting Services, Newport, Mich. -- Consulting-Specifying Engineer, 5/1/2006

If you haven't heard of PAPA yet, you soon will. Here's a brief history of what it is and how it came to be.

PAPA is an acronym for positive air pressure attenuator. The devices are currently available only for sanitary drain and vent systems designed to the "engineered systems" portions of the plumbing codes and sealed by a professional engineer.

The technology was developed at the School of the Built Environment at Heriot Watt University in Edinburgh, Scotland by Professor John Swaffield. He was looking for a solution to positive pressures in all types of sanitary drainage systems as part of research he was conducting for certain air-admittance valve manufacturers. In high-rise applications, positive air pressures build up near the base of all sanitary waste stacks, and the positive pressures need to be relieved.

Professor Swaffield set out to develop a device that would connect to the drainage system and absorb these positive pressures. Typically, positive pressures build as the waste falls down the stack and pulls the air with it. The resulting fluid flow causes a positive pressure ahead of the slug of waste and a negative pressure behind the flow of waste. In a single-stack system where there is no relief vent near the base of the stack, pressures can really build up.

Swaffield came up with the idea to place a flexible material in an enlarged vented chamber to create a giant air hammer arrestor—similar to a large bellows or balloon—in the piping and absorb the positive pressures in the drainage stack. He sent his research assistants out to look for an appropriate material to use in the device. They came back with balloons, hot water bottles and plastic bags, among other things. Eventually, they decided they needed something larger and sturdier, so they contacted a manufacturer of automobile inner tubes to make a few prototypes of what looked like an oversized hot water bottle. The bladder fits inside a 6- or 8-in. diameter pipe and is fastened to the drainage pipe on one end. This solution eventually worked out great for the adventurous researchers. Hence, PAPA was born.

In the spring of 2003, I had the opportunity to visit the Heriot Watt University research lab where I witnessed a demonstration of a PAPA device on the lab's 20-story test stand. The first test was conducted on a single-stack drainage system without a PAPA device. The positive pressures generated blew the test water out of a series of 1-1/2-in. glass traps on the lower floors of the test stand. The next test was conducted with one PAPA device installed on the stack. It maintained pressures to less than two inches of water column and kept the traps from blowing out. When they added a second PAPA device, it kept the pressure fluctuations within the code-required one inch of pressure fluctuation.

PAPA devices are available in the U.S. and are distributed by Studor, Inc., a manufacturer of air-admittance valves. They're great for controlling pressure fluctuations in all new sanitary drainage systems and can be used on existing drainage systems as well. Additionally, they can be installed vertically or horizontally off a wye branch on the stack.

Look for PAPA devices to show up in the standard-development process and in the codes over the next few years.