2-Way Valves
A 2-Way Unbalanced Single Seat Valve is the simplest and lowest cost solution for sizes 3” and under. This type of body is available in both screwed and flanged ends in a variety of materials. A variation of this design is the Cage-Retained Seat Valve that is also unbalanced. These are used in aggressive applications where trim replacement is a desired maintenance objective. The Cage-Retained Seat Valve has a bolted bonnet, and in some cases as with a specification, a body style that is chosen for you.
This reference is for those who prefer to choose their own.

A 2-Way Balanced Valve is the most economical solution for sizes over 3” or when higher inlet pressures are involved. Balanced valves have significantly less force to overcome as compared to an unbalanced application. Therefore, smaller and lower cost actuators can be used to open, throttle, and close the valve. On larger valves, actuators make up an increasing portion of the cost.

There are two balanced valve varieties: 1) Double Seat and 2) Cylinder Balanced. A double seat valve allows for dirtier fluids and the least amount of actuation force possible. A drawback is that manufacturing tolerances allow for ANSI Class III
shutoff only. The Cylinder Balanced design relies on an o-ring seal and therefore, cleaner fluids are required. There is also some additional friction of the seal to overcome upon actuation. However, ANSI Class IV shutoff is the standard.

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Rotary 2-Way valves are often the choice in larger sizes, in part because of price.
Flow patterns in our eccentric plug valve allow for much higher Cv’s, size for size, compared to linear stroking globes. These valves also have a smaller footprint with less metal involved. Rotary 2-Way valves are particularly suited for higher viscosity fluids with their straight-through flow path and can tolerate erosive or corrosive fluids with the specialty materials offered. Some long-time professionals take exception to this type of control valve as something less than pure, from a flow to stroke measured characteristic. However, this type of valve has served a variety of industries very well for several decades. One inherent drawback for some applications is higher dB sound levels in high differential pressure applications.

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3-Way Valves
3-Way Valves come in two varieties: 1) Mixing Only, with a common out the side,

2) Diverting, with a common in the bottom. In some cases, existing plumbing considerations may help choose the profile. When cost is the top consideration, the Mixing Only profile is the lower cost solution for mixing, yet for bypass applications, this may require specific piping designs. The diverting valve can be flowed backwards for mixing when that piping arrangement is desirable, but is less stable near the seat.