The unique electric switch design in the 1640 is another Dwyer Instrument, Inc. innovation. The Dwyer® Model 1640 Differential Pressure Switch resembles the Series 1630 switches. The Model 1640, however, is equipped with a single pole, double throw floating contact switch (not snap acting) so it functions as a null switch.

Drawing shows the switching action schematically. As the diaphragm moves in response to pressure changes, it moves the floating contact to cause switching action at two preset points with no switching action between these points. The "high" circuit will be closed when rising pressure differential reaches the preset level. The "low" circuit will be closed when falling pressure differential reaches the preset level.

A typical example of usage is to position motorized dampers when static pressure in a duct system reaches a desired maximum and reposition the dampers when the static pressure falls to a pre-established minimum. By using a pitot tube sensing element the Model 1640 switch can serve in the same way to control air velocity and maintain a constant volume of air in a supply duct.

CAUTION: FOR USE ONLY WITH AIR OR COMPATIBLE GASES.

SPECIFICATIONS
Service: Air and non-combustible, compatible gases.
Wetted Materials: Consult factory.
Temperature Limits: -30 to 110°F (-34.4 to 43.3°C).
Pressure Limits: 10 psig (68.95 kPa) continuous, 25 psig (172.4 kPa) surge.
Switch Type: Single-pole double throw (SPDT) floating contact (not snap action).
Electrical Rating: Non-inductive - 2.5 A @ 110 VAC, 1.5 A @ 220 VAC, 1 A @ 24 VDC, 0.5 A @ 110 VAC; Inductive - 1 A @ 110 VAC, 0.5 A @ 220 VAC, 0.5 A @ 24 VDC. (De-rate 70-80% for very slow pressure changes.)
Electrical Connections: 3 screw type, common, normally open and normally closed.
Process Connections: 1/8" female NPT.
Mounting Orientation: Diaphragm in vertical position. Consult factory for other position orientations.
Set Point Adjustment: Screw type.
Weight: 4 lb 13 oz (2.18 kg).
Agency Approvals: CE.

Adjustment of the Switch
The "high" actuation point of the Model 1640 switch is indicated on a calibrated scale secured to the transparent range screw enclosure. Resetting is accomplished simply by turning the adjustment screw with a screwdriver to the desired setting on the scale.

The "low" actuation point is set by adjusting the span of the null by turning the Span Adjusting Screw on top of the switch element inside conduit enclosure (see photo).

Typical Wiring Hook-Up
Rising pressure closes the "high" contact which causes the motor to rotate in a counterclockwise direction. Decreasing pressure closes the "low" contact and causes the motor to rotate in a clockwise direction. When the floating contact is in the null zone there is no switching action and motor is at rest.

CAUTION: Because of the very low electrical rating, the 1640 switch is almost always used with a relay which has suitable current carrying capability.

OPTIONS -- Consult Factory for Pricing

-WP Weatherproof Housing.
-EXPL Explosion-proof Housing.