The Caleffi 519502A is a 519 Bypass Valve differential pressure bypass valve with 3/4" NPT connections.
Best for zoned systems where closing zone valves would otherwise starve the circulator.
Specifications sourced from Caleffi North America technical literature. Last reviewed July 2026.
Key Features
Protects Circulators at Low Flow
As zone valves close, the bypass opens to maintain minimum circulator flow, preventing pump noise, cavitation and premature wear.
Adjustable Differential Setting
The bypass setpoint is field-adjustable, so the valve can be matched to the circulator curve and the design differential of the system.
Technical Specifications
| Product Type | Differential Pressure Bypass Valve |
| Connection Size | 3/4" |
| Connection Type | NPT |
| Series | 519 Bypass Valve |
| Maximum operating pressure | 150 psi |
| Medium temperature range | 32-230 deg F |
| Material | brass |
| Shipping Weight | 1.0 lb |
Documentation
Related Products
- Caleffi 519566A : 519 Bypass Valve 3/4" Press
- Caleffi 519599A : 519 Bypass Valve 3/4" Press/Sweat
- Caleffi 519600A : 519 Bypass Valve 1" female NPT inlet x 1" male NPT union outlet
- Caleffi 519609A : 519 Bypass Valve 1" female NPT inlet x 1" press/sweat union outlet
Frequently Asked Questions
What does Caleffi 519502A do?
It maintains minimum circulator flow as zone valves close. Without a bypass, a circulator can be left pumping against a nearly closed system, which causes noise, cavitation and premature wear.
Is the setting on Caleffi 519502A adjustable?
Yes. The differential setpoint is field-adjustable so the valve can be matched to the circulator curve and the design differential pressure of the system.
What connection does Caleffi 519502A use?
It is supplied with 3/4" NPT connections. Other sizes and connection styles in the 519 Bypass Valve range are listed under Related Products.
What are the pressure and temperature limits of Caleffi 519502A?
Maximum operating pressure is 150 psi.
What is the warranty on Caleffi 519502A?
Caleffi covers this product under its standard two-year limited warranty against defects in material and workmanship from the date of shipment. ZOT Supply is an authorized Caleffi distributor.
- Product Type:
- Differential Pressure Bypass Valve
- Series:
- 519 Bypass Valve
- Product Family:
- Differential Pressure Bypass
- Connection Type:
- NPT
- Connection Size:
- 3/4 inch
- Max Operating Pressure:
- 150 psi