Pneumatic Control Valves

Design and principle of Operation
The Type 3345-1 and Type 3345-7 Pneu-matic Control Valves consist of a Type 3345
Diaphragm Valve and either a Type 3271
Pneumatic Actuator or a Type 3277 Pneu-matic Actuator for integral positioner attach-ment.
The diaphragm stem (6) of the valve dia -phragm is connected to the actuator stem (8.1) by a stem connector (7) or they are Screwed together (in the stainless steel ver -sion up to DN 25). To protect the valve dia -phragm, stoppers (4 and 6.3) are fitted at The top and bottom of the actuator stem.
The process medium can flow through the Valve in both directions.
The position of the Valve diaphragm (3) determines the flow rate Through the valve.
The position of the diaphragm stem (6) is Changed by the signal pressure acting on the Diaphragm of the actuator.

Fail-safe position
The control valve provides two different
Fail-safe positions depending on the arrange -ment of the springs in the actuator:
Actuator stem extends
When the signal pressure is reduced or the Power supply fails, the springs move the AC-tuator stem downwards and close the valve.
When the signal pressure increases again, The valve opens acting against the force of The springs.
Actuator stem retracts
When the signal pressure is reduced or the Power supply fails, the springs move the AC-tuator stem upwards and open the valve.
When the signal pressure increases again, The valve closes acting against the force of The springs.
2 Assembling valve and actuator
If the valve and actuator have not been as -sembled together by the manufacturer, or if
The actuator of a control valve is to be re -placed by an actuator of another type or an-other size, proceed as described below.
2.1 Type 3271 and Type 3277
Actuators
1. Undo the lock nut (6.2) and stem connec-tor nut (6.1) on the diaphragm stem and Thread them downwards.
Pull the diaphragm stem upwards.
2. Remove the stem connector clamps (7) And the ring nut (8.2) from the actuator (8).
Slide the ring nut over the diaphragm Stem.
3. Place actuator onto the valve bonnet (5) And secure with the ring nut (8.2).
4. Read bench range and fail-safe action From the actuator's nameplate (e. G. 0.2
To 1 bar and "Actuator stem extends"). In This case, 0.2 bar corresponds to the
Lower bench range value to be adjusted
And 1 bar corresponds to the upper Bench range value.
The fail-safe action "Actuator stem ex -tends" is indicated on the Type 3271 AC -tuator by FA and "Actuator stem retracts"
By FE. The Type 3277 Actuator bears the Corresponding symbol.