Dry Fire Hydrant Design 20 - Jet Assist DFH - Dadeville, Alabama
 
By President Mark Davis
December 6, 2018
 

This week's news story shares some photos from a "jet-assist" dry fire hydrant installation that was completed by Stan Merrett (ETT, LLC) several years. The installation was completed at Lake Martin in Dadeville, Alabama and work shown was a prototype at the time.

The installation runs out into the lake 186 feet and since the lake is drawn down about 10 feet in the winter there can be upwards of 15-feet of lift at times. To help counter the lift problem, the dry fire hydrant design has three "jets"...one about every 60-feet. The 2-1/2-inch down-feed connection to the jets begins with 4-inch pipe and reduces in size as it goes along the length of the suction pipe.

The installation has an 8-inch horizontal strainer with check valve in front. The first jet is in front of the strainer. The system also has a built-in relief valve set at 15 psi so that the system cannot be over-pressurized and blow apart suction hose connected to the suction pipe.

During early testing, the folks obtained around 650 gpm net gain from the installation at a lift of around 14-feet. Higher flow would have been attained had 8-inch pipe been used to make the entire run...it was not available, so only 80-feet of the system used 8-inch pipe.

Many thanks to Mr. Merrett for taking the time to share his work on this interesting design.

 
The system contains a relief valve designed to blow-off at 15 psi so as not to damage suction hose.
The system contains a relief valve designed to blow-off at 15 psi so as not to damage suction hose.
This unique DFH design uses the venturi "jet" principle to help combat lift issues in this system.
This unique DFH design uses the venturi "jet" principle to help combat lift issues in this system.
 
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Installation day preparation.
Installation day preparation.
Testing to ensure it works.
Testing to ensure it works.
 
One of the three jets is located close to the 8-inch suction strainer.
One of the three jets is located close to the 8-inch suction strainer.
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The trash bag was used to help float the system out into position.
The trash bag was used to help float the system out into position.
 
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