Overview
The Dwyer 1638-2 is a precision large diaphragm differential pressure switch designed for HVAC systems and process control applications. This switch monitors pressure differentials between two points in a system and triggers an electrical response when the pressure exceeds a user-defined setpoint. The Dwyer 1638-2 combines robust diaphragm construction with easy-to-use visible setpoint adjustment, making it ideal for filter monitoring, duct pressure control, and equipment protection in air handling units.
Key Features
- Visible Setpoint Adjustment: Easy screw-type adjustment with enclosed scale for simple and repeatable setpoint changes.
- Large Diaphragm Design: Sealed, leak-proof construction maximizes reliability and precision across the operating range.
- SPDT Contact Configuration: Single-pole, double-throw contacts provide both normally open and normally closed control.
- High Electrical Rating: 15 A capacity at 120–480 VAC (60 Hz) eliminates the need for external relays in most applications.
- Certifications: UL and CSA listed, FM approved for general service ensures code compliance in residential and light commercial installations.
Technical Specifications
- Pressure Range: 1.0–3.0 inches of water column (w.c.)
- Setpoint Adjustment Range: 0.05–12″ w.c. (5 standard ranges available)
- Accuracy: ±1% repetitive accuracy
- Electrical Rating: 15 A @ 120–480 VAC, 60 Hz (1/8 HP @ 125 VAC; 1/4 HP @ 250 VAC)
- Switch Type: SPDT (Single-Pole, Double-Throw) snap-action
- Deadband (Approx.): 0.06″ w.c. minimum setpoint, 0.08″ w.c. maximum setpoint
- Pressure Limit: 10 psig continuous; 25 psig surge
- Temperature Range: −30 to +110 °F
- Connection Type: 1/8″ NPT female (two ports)
- Electrical Connections: 3 screw-type terminals (common, normally open, normally closed)
- Mounting: Diaphragm mounted vertically; consult factory for alternative orientations
- Service Medium: Air and non-combustible, compatible gases only
Typical Applications
- HVAC Filter Monitoring: Detects clogged air filters and triggers replacement alerts or fan shutdown.
- Duct Pressure Control: Maintains optimal static pressure in supply or return ducts to improve system efficiency.
- Damper Control: Activates motorized dampers to balance airflow across multiple zones.
- Equipment Protection: Monitors pressure differentials across heat exchangers, condensers, and other sensitive components.
- Industrial Process Applications: Suitable for general pressure monitoring in pneumatic and gas systems (air/compatible gases only).
Compatibility & Replacements
Compatible With
- Standard HVAC control systems and building automation platforms
- Most 24 VAC or 120 VAC switching relay circuits
- Pneumatic and low-pressure gas control loops (air and non-combustible gases)
- Filter status monitoring and alert systems
Replaces / Drop-In Replacement For
- Other Dwyer Series 1630/1638 variants with similar pressure ranges
- Generic large diaphragm differential pressure switches in the 1–3″ w.c. range
- Verify compatibility with your system integrator or OEM before ordering to ensure port connections and setpoint range match your application.
Works With
- Building automation systems (BAS) and direct digital controls (DDC)
- Pneumatic control logic and relay switching circuits
- HVAC service tools and pressure measurement devices (analog gauges, digital manometers)
- Standard electrical enclosures rated for 120–480 VAC operation
