A Simple Explanation of the Construction and Operation ofFire Hydrants

A Simple Explanation of the Construction and Operation ofFire Hydrants

This is the fourth section of an article which describes some of the more common makes of fire hydrants.

HYDRANTS are comparatively simple devices. They contain no complicated gears or combinations of machine forms. They are free from inaccessible parts, and yet few can honestly confess they understand the construction of fire hydrants.

Primarily a hydrant is a pipe extending from the underground water main, plus a device for obstructing the flow of water so that water may be obtained when desired, and outlets to which the Fire Department may connect hose lines for its supply. Few devices can be simpler.

Hydrants, when properly installed, require little attention. As a guarantee of good service, they should be examined in the spring and in the fall, and each time that they have been used during freezing weather.

Just as in automobiles, there are various makes of hydrants on the market, and in many cities, it is possible to find several makes in use. An appreciation of the mechanics of all the leading makes is therefore advisable. In the two previous issues were described some of the common types of hydrants.

Ludlow Hydrant

Lower Section and Sketch of the Ludlow Hydrant

The Ludlow Diamond hydrant (Ludlow Valve Manufacturing Company, Troy, N. Y.) has a slide gate hydrant valve with a locking device that prevents the flow of water in case the hydrant barrel is broken. The device operates the moment the gate is closed and the drip opens. It is released upon starting to open the hydrant.

The drip valve is screwed to the lower end of the hydrant stem. It works in a cup set in the extreme bottom of the hydrant. It opens after the gate is closed and wedged, and closes before the gate is released. It never leaves the drip cup and revolves with every movement of the stem. Both the gate and drip valves are faced with rubber.

The hydrant body ends in a flange at the ground line. The hydrant has thicker metal at points A, B and C to reinforce the body horizontally. Stresses and dimensions have been calculated, the designers claim, so that in the event of impact, breakage will occur directly above the ground.

Then when it becomes necessary to replace the hydrant the bolts are loosened which connect the hydrant flange to the connecting barrel flange, the old hydrant body is taken off, the stem straightened or replaced, and a new hydrant body set in place.

The hydrant top and the nozzle caps have plain beveled surfaces, semi-phosphorus aluminated coated, to reflect light so that the hydrants are easily distinguished by the motorist and the approaching fire company.

Mathews Hydrant

Section of Mathews Hydrant

The barrel of the Mathews Hydrant (R. D. Wood & Co., Philadelphia, Pa.) contains all the working parts. The barrel, complete with the interior mechanism, can be removed intact by unscrewing it from the elbow and withdrawing it through the protection case of the hydrant.

The operating nut is shielded to keep out moisture and dirt. The threaded portion of the stem is above water and may be oiled through a hole in the operating nut. A stop nut is provided to arrest the downward travel of the stem before it can strike the bottom of the elbow and cause the stem to buckle due to excess pressure.

The nozzle direction may be changed by loosening bolts in a swivel flange which permits the hydrant head to be turned. This swiven flange, at the base of the nozzle section, enables nozzles to be faced at any point in the complete circle.

The drain valve, its guide and upper main valve plate are cast in one piece. It is rigidly keyed to the hydrant stem and moves vertically in connection with the main valve. The drain valve is faced with leather held in place by six copper rivets. The main valve is fastened securely to the hydrant stem and does not revolve. It moves away or toward its seat as the hydrant is opened or closed. The main valve is built up of several layers of leather. The main valve assembly is cone-shaped to cause a gradual opening or closing of the hydrant and the elimination of water hammer.

When a hydrant is broken, the head is removed so that workmen can get at the lower part. A tubular lug wrench is slipped down over the barrel to engage four heavy lugs that are cast on the outside of the barrel at the base. The broken barrel is unscrewed from the elbow and the lower end of the broken hydrant is removed. A new hydrant, complete, is inserted and screwed into place. The bolts on the swivel flange are then loosened and the revolving head turned so that the nozzles are facing in the proper direction. The bolts are tightened and the installation is completed.

A special extraction tool has been designed for removing broken barrels of the older type of Mathews hydrants.

The manufacturers claim that with this type of product, the entire job of removing a broken hydrant barrel and replacing it with a new one, can be done in about thirty minutes without recourse to digging.

(To be continued)

No posts to display