158 WATER CONDUCTORS AND ACCESSORIES 



allowing the air to escape. As the water returns, it lifts the float 

 thereby closing the valve. 



The poppet valve, on the other hand, is intended for use on 

 pipe lines to permit air to enter when water is being drawn off 

 and thus eliminates any danger of collapse from vacuum forming 

 in the pipe lines as, for example, when the head gates are closed. 

 Similarly, they may be provided to allow air to escape when the 

 pipes are being filled. The valve remains open until the water 

 reaches and lifts the copper float and closes the same, after which 

 it remains closed while the pressure is on.. 



