28. September 2012 10:15
One of the tasks assigned to your fire company is the annual inspection of fire hydrants in your district. All the hydrants that you have tested are dry-barrel hydrants. You replace all the hydrant caps except one. As you are closing the stem on one hydrant, you shut it completely, open it a quarter turn, and place the palm of your hand over an open discharge. You feel a slight suction on your hand. You close the hydrant stem completely, replace the discharge cap, and complete the inspection.
What is the purpose of dry-barrel hydrants?
Answer: Dry-barrel hydrants are used in areas that experience prolonged periods of subfreezing weather. The control valve is located below the frost line underground and prevents water from entering the hydrant barrel and freezing, making the hydrant inoperable.
What causes the slight suction on your hand?
Answer: It is an indication that the water is draining out of the dry barrel through the drain hole at the bottom of the hydrant.
What conditions should you look for during a hydrant inspection?
Among the items listed in the text, you should inspect the hydrants for:
Obstructions, such as sign posts, utility poles, weeds, bushes, or fences that might interfere with pumper-to-hydrant connections or with opening the hydrant valve.
Outlets that face the wrong direction for pumper-to-hydrant connections.
Insufficient clearance between outlets and the ground.
Damage to the hydrant.
Rusting or corrosion.
Outlet caps missing or stuck in place with paint.
Stem nut that cannot be turned or turns feely with no visible result.
Obstructions (bottles, cans, rocks) inside the hydrant outlets.
Damp ground surrounding the hydrant or erosion indicating a drain valve leak.
Hydrants painted by property owners (caps adhered to threads by paint).
By Rob Rosovich, Fire Protection Engineer