Durabilty is an important consideration when selecting a valve for an irrigation system. If adverse conditions exist, such as high pressure, high velocity, or surging, the valves should be rated for heavy duty operation. On the other hand, if conditions are ideal, a valve rated for light comercial duty will suffice.

While several factors contribute to overall strength and durability of a valve, the composition of the housing (body and bonnet) is at the top of the list. Based on composition, irrigation valves fit into three main categories:

• PVC (poly-vinyl-chloride)

• glass-filled nylon

• brass

PVC

Manufacturers generally recommend their PVC valves for use in one or more of the following applications: residential, light commercial and commercial.

Pressure ratings vary from 125 p.s.i. to 150 p.s.i. Models in 3/4-inch and 1-inch sizes are often sold at amazingly low prices due to very strong competition for the huge residential market. Do-it-yourself retail outlets routinely have them on sale for as low as $9.97. Larger sizes, 1 1/2-inch and 2-inch, are available primarily through wholesale irrigation distributors.

Glass-filled Nylon

Valves constructed of glass-filled nylon are available in 3/4-inch through 3-inch sizes and are rated by manufacturers for heavy duty residential, commercial and institutional applications. The superior strength of glass-filled nylon enables these valves to perform under more challenging conditions than would normally be recommended for PVC valves.

Pressure ratings from manufacturers vary from 150 p.s.i. to 220 p.s.i. To ensure that the bonnet will remain securely fastened to the body in high-pressure conditions, either brass inserts or studs are molded into the body of most models. Brass inserts serve as anchors for bonnet screws or bolts, while studs (brass or stainless steel) fasten to the hex nuts that screw down onto the studs from above the bonnet.

Brass

The strongest and most durable irrigation valves are made of brass. Up and down the state of California, there are school districts where brass hydraulic valves installed in the 1950s and 60s are still in operation. Although interior parts have been replaced in most of them, the brass housings have endured.

Not surprisingly, brass valves are more expensive than plastic valves. In many parts of the country the demand for brass valves is small and virtually non-existent in the residential market. There are noteable exceptions, particularly in California.

Throughout California, brass valves are predominant in the institutional sector (school districts, universities, parks, freeways, military bases, prisons, etc.). In many parts of the state the demand for brass valves is also very strong in the residential and commercial markets, particularly in Southern California, where most wholesale irrigation distributors carry a large inventory of in-line brass valves and brass actuators. High water pressure has a lot to do with it. In the San Fernando Valley, for example, water pressure averages over 125 p.s.i., and in some sections exceeds 200 p.s.i.

Be careful not to pay a premium for valves that may be overrated, or underrated, for given conditions.

Got an idea for an Irrigation Talk topic? E-mail it to jfultz@landscapearchitect.com. We welcome your input!