In June 2006 Valmatic engineers tested different interior valve coatings at the Salt Creek Sanitary District Water and Waste Treatment Plant, Illinois, USA. The aim of the experiment was to find out which coating provided the most protection against harmful build-up and deposits in a wastewater application.

Four, 2” Valmatic 802A combination air valves with different coatings were installed in to the plants system.  The different coatings were as follows; FBE coating (fusion bonded epoxy), Teflon coating, Two-Part Expoxy coating and no coating (to serve as the independent variable).  The combination valves were all of cast iron construction with 316 stainless steel trim and were coated prior to assemble and tested with AWWA C512 before installation.

How the Combination Air valves work

Normally, the valve’s outlet is open and designed to exhaust air during pipeline filling. It automatically closes when fluid enters the valve and causes the stainless steel float to rise, therefore lifting the stainless steel plug against the Buna-N seat.  The valve is used to release air during system start-up and accumulated air during system operation, as well as allowing air to re-enter the line upon system shutdown or failure. The combination air valve also provides protection from pipeline vacuums by allowing the valve to open as negative pressure develops, admitting air back into the line. This feature reduces the potential for surges created by column separation. Finally, the design of the valve body is elongated to prevent sewage from interfering with the upper mechanism and the bottom of the body is sloped toward the inlet to reduce the build-up of debris.

The Experiment:

The four combination air valves were fitted in a valve vault opposite a submersible pimp wet well, downstream from the pumps and upstream from the check valves.  The pumps run every few minutes except during rainy periods when they may all run continuously.  Each valve was installed on a raw sewage main which ran parallel to the vault.  The valves were exposed to harsh raw sewage which was pumped directly from the plants mechanical screens.

The Results:

One Month after Installation

The four valves were inspected and tested one month after installation to check they were functioning properly.  None of them had sludge build ups and none of the parts had been damaged or worn.  Over the following three years the valves were checked periodically for performance.  The valves saw equal usage over the three year period.  There were no problems with valve operation and no backwashing or maintenance was required.

Three Years after Installation

In July 2009 the valves were completely removed from the system and inspected.  All four valves still had the factory epoxy or blue primer coating and did not exhibit excessive corrosion.  Each valve cover and float mechanism were lifted from the valve and documented. There was no damage or wear to any of the valve mechanisms. All four of the valves were operational and there was no clogging in the valve mechanism or the valve inlet.

The Conclusion:

After three years of use all four 2” Valmatic Combination Air Valves were effective in exhausting and admitting air in the 10-inch pump discharge lines and assisted in quiet check valve operation.  The machine supervisor at the treatment plant said “the air valves were essential in preventing slam in our check valves and they operated for three years in raw sewage without the need for backwashing or maintenance.”

So despite the type of coating all four valves performed to satisfaction in a wastewater application.  The valves with coated interiors showed more resistance to sludge and debris build up compared to the standard valve.  The FBE coating provided the greatest overall level of protection and the uncoated 316 stainless steel float had greater resistance to buildup of sludge or debris than the coated floats.  Due to the satisfaction of the water plant in their performance and low maintenance the valves are still installed.

Their innovative design has meant no need for backwashing in four years of service.  The extended valve body prevents solid material for reaching the operating mechanism and the bottom is sloped toward the outlet to prevent clogging. The smooth interior coating options are able to withstand harsh wastewater applications, thus reducing the frequency of maintenance. In this application and interior coating comparison, the fusion bonded epoxy (FBE) proved superior.

To discuss the findings of this case study further or discuss how Valmatic Valves can be utilised in your application, please call our technical team on +44 (0) 8444 501123.