Control Valves

1. What is a Control Valve?

2. What type Control Valves does Robertshaw Offer?

3. Where are Robertshaw Control Valves used?

4. What do I need to know to select the proper valve?

5. How do Robertshaw Control Valves work?

6. How do I size my control valve?

7. How do I make a quick temperature control loop?

1. What is a Control Valve?

Control Valves are among the most common final control elements in a classic control loop. A control valve is a variable orifice or restriction device that can be installed in piping.

2. What type Control Valves does Robertshaw Offer?

Robertshaw Control Valves are diaphragm actuated pneumatic control valves with globe style bodies.

The multi-spring actuator styles VC230A/VC231A are very versatile 30 - sq. in. diaphragm actuators. They are offered in direct- or reverse-acting styles and are field reversible. They can accommodate a variety of valve assemblies ranging from narrow reduced port styles to 6 in. 3-way styles.

The 10 - sq. in. Model VC-210 is also quite versatile and is bellows sealed. It is available with direct-, reverse-, or 3-way action, and in brass or stainless steel constructions.

3. Where are Robertshaw Control Valves used?

Generally, our valves are used for control in light industrial applications such as low-pressure steam, water, or air. A great number of applications exist for virtually any type of wet process including pigment & dye machinery, commercial buildings, natural gas pipelines, food & beverage, etc.

4. What do I need to know to select the proper valve?

Each of the following needs to be considered separately for proper selection:
a. Materials of construction: brass, stainless steel, steel, other
b. Style: 2-way, 3-way, class of shut off, number of ports, etc.
c. Characteristics: quick opening, linear, equal percentage
d. Size: size of connecting pipe, Cv (the engineering size coefficient) necessary to meet flow requirements
e. Actuator: size, action
f. Accessory equipment: positioner, I-P transducer, solenoid, etc.

See Control Valve Selection Guide for further details

5. How do Robertshaw Control Valves work?

Robertshaw diaphragm actuated control valves are designed to control the flow of a fluid passing through a valve by responding to a pneumatic signal from an instrument or pilot controller. The opening, closing and throttling action of the valve is controlled by changes in the instrument output pressure as it responds to changes in the system being controlled.

6. How do I size my control valve?

Size is probably the most critical element in valve selection. Undersized, a valve will not yield enough flow. Oversized, it will not give proper control. To select the correct valve size:

a. Find the Cv (the engineering sizing coefficient) of the valve. Using the information of pressure drop, flow, viscosity, specific gravity, etc., calculate the required Cv using a formula, sizing program, or the Robertshaw “Flo-Rule”. (Cv=gpm of water at 1 psi pressure drop)
b. Choose the proper valve according to the product specifications, or reference the Control Valve Selection Guide.
c. A valve sizing “Rule-of-Thumb”: For proper control, a valve should be one to two sizes smaller than the pipe to which it is being fitted.

7. How do I make a quick temperature control loop?

Incorporate a Robertshaw Self-Actuated Temperature Regulator into your system. Another quick and easy method to design a temperature control loop is to install a Robertshaw DT-700 Fultrol Pilot Temperature Controller and a VC-210 Control Valve. Both units are normally carried in stock and available for immediate shipment.