AVK free flow hydrant for quick relief of water supply line

A comprehensive refurbishment of a DN500 drinking water supply line has taken place in the Stadtwerke Herford municipality in the western part of Germany.

Replacement of a DN500 gate valve

The water supply line comprises a total length of five kilometers and as a first step of the refurbishment, a DN500 gate valve was replaced. Due to a long lifetime it had stopped functioning properly and a new gate valve with by-pass was mounted instead. To replace the old gate valve, the old ductile iron pipe was cut and disconnected from the valve.

The importance of saving time

Maintenance and refurbishment of such a major supply line always implies certain obstacles to the public and to road traffic and it has in general high costs. Thus, it is of great importance that these activities are carried out as time-saving as possible.

Free flow hydrant for drainage

A supply line of such a large dimension always remains half-filled after a shut-off, and drainage of the line in the usual way using a standard hydrant takes a lot of time. An AVK free flow hydrant was mounted via a T-piece that was flanged directly to the gate valve and due to the full bore of the hydrant, a self-priming pump could easily be inserted to help drain the line. By means of this self-priming pump together with the free flow hydrant, an additional volume of 36 m³/h could be drained from the line.

After the successful installation, Stadtwerke Herford have planned to use additional AVK free flow hydrants and gate valves for other parts of the supply line as well.


Summary of technical features

Free flow of the medium 
Operation mechanism outside of medium 
Enhanced flow rate 

157 m³/h at 1 bar differential pressure to VP325 
216 m³/h at 1 bar differential pressure to EN14339 

Easy insertion and retrieval of pipe inspection and maintenance equipment 
Inside bore 80mm 
Smallest narrowing 71mm – bayonet 

Improved corrosion protection 
Castings: Minimum 250μm coating to GSK guidelines  
Stainless steel pipe: Material W1.4307 (AISI 304L) – reduced carbon < 0,03%, additional outside EPOXY coating (min. 100μm), internally passivated

Summary of technical features

Hydrant is insensitive to hard particles  
Valve rotary plate of stainless steel with additional antifriction coating 
Coating reduces friction and thus torque 
Coating protects against adhesion 
Operation mechanism with high torque protection 
To EN 1074-6: MST 210 Nm 
To Belgian standard: MST 280 Nm 
Automatic „brake” reduces load on stem nut and valve rotary plate 

Automatic drainage 
Residual water vol. < 10ml (100 ml to EN 1074-6) 
Drainage time 30 sec. (15 min. to EN 1074-6) 
Flush-proof to VP325