Caleffi 519500 3/4 Inch Adjustable Differential By-Pass Valve

The 519500 is a 3/4 inch adjustable differential by-pass valve from Caleffi with a setting range of 10 to 60 kPa (1 to 6 metres of water gauge). Fitted across the flow and return of a variable-flow circuit, it opens only when the pump pressure exceeds the set value and lets the surplus water recirculate, protecting thermostatic valves from noise and keeping the pump near its design point.

A relief path for variable-flow circuits

When thermostatic valves or two-way motorised valves close, a fixed-speed circulator pushes the same flow into fewer open paths and pressure climbs. The by-pass valve gives that flow somewhere to go. A compression spring, adjusted with the control knob, holds the obturator shut until the differential pressure generates more thrust than the spring; the obturator then opens and the by-pass circuit discharges the excess. The datasheet notes the trigger pressure stays more or less constant as the discharge flow changes, which is what makes it useful as a limit.

Key features from the datasheet

• Adjustable with a graduated scale in metres w.g.; the setting is locked with a fixing screw once found
• Used with thermostatic valves, 2-way motorised valves and heat pump systems
• In heat-pump circuits it can guarantee the minimum flow rate a machine or variable-speed circulator needs for correct operation
• Brass body with EPDM obturator and O-ring seals; stainless-steel spring; ABS knob
• Union connection with non-asbestos fibre seals
• Valve opens only when the set differential pressure is exceeded, at any closing condition of the system valves

Technical specification

Selection and ordering guide

The 519 series has six codes spanning three connection types and three setting ranges. Pick the range from the pump pressure: low-pressure residential circuits use 10 to 60 kPa, while larger pumps need the higher ranges.

The straight 519015 has a lower temperature limit of 0 to 100 °C; the others reach 110 °C.

Setting procedure and installation

• Apartment-style system: with the regulating valves fully open, set the by-pass to its maximum value, close about 30 % of the thermostatic valves, then gradually open the by-pass with the knob until hot water is felt in the by-pass line.
• Re-open the thermostatic valves and check that the by-pass line stops flowing, then lock the knob with the fixing screw.
• Heat-pump system: select and calibrate the valve from the heat-pump circulator data plate so the minimum flow is maintained.
• The by-pass should pass enough flow to hold the pump at its nominal point when the first valves close; check that sizing before installation.
• The hydraulic-characteristic diagrams show the trigger pressure against flow for each code.

Applications in Gulf heating and cooling circuits

Differential by-pass valves are the low-cost protection on small and medium fixed-speed circulator systems, such as villa and apartment heating loops, small chilled-water zones with thermostatic fan coils and heat-pump or chiller circuits that need minimum flow. In Oman and the GCC the by-pass is a common fit on package chiller loops where the load falls at night. The datasheet limits the glycol content to 30 % and the temperature to 0 to 110 degrees C, so large process systems need different equipment.

Selection and installation notes

Hydronic components are selected from the design flow, the pressure drop and the maximum working pressure and temperature of the circuit. Check the connection size and thread type, fit isolating valves so the part can be serviced, flush the pipework before commissioning and respect the flow direction marked on the body. Insulate heating and chilled-water parts according to the project specification.

Information needed for a quotation

Send the full model code, the quantity, the delivery location in Oman or the GCC, the intended use and any accessories needed, so that the complete package can be quoted together.

Documents and supply information

The manufacturer data sheet is attached to this page and should be read together with the project specification and the site risk assessment before a purchase is confirmed. Ratings, standards and dimensions are quoted as printed on that sheet. Lead time, stock position and certificates available with the shipment are confirmed in the quotation, and we supply to Oman and the wider GCC region for industrial, utility and building services projects.

Related items

The 519 series does not need electrical connection. Related Caleffi balancing and pressure-control valves, such as the 132 balancing valve with flow meter and the 140 differential pressure regulating valve, are separate datasheets and are quoted individually.

Frequently asked questions

What does a differential by-pass valve do?

It stays closed until the pump differential pressure exceeds the set value, then opens and recirculates the excess flow so the pump pressure stays limited when valves close.

What is the setting range of the 519500?

10 to 60 kPa, which equals 1 to 6 metres of water gauge, set with the graduated knob and locked with a screw.

Can it protect a heat pump?

Yes. The datasheet describes by-pass valves guaranteeing the minimum flow rate that a heat pump or variable-speed circulator needs, calibrated from the circulator data plate.

What medium and temperature are allowed?

Water or glycol solutions up to 30 percent, at 0 to 110 degrees C and up to 10 bar.

Who supplies the Caleffi 519500 in Oman?

Seven Star LLC is an independent supplier in Muscat and quotes against the exact code. Confirm the setting range and connection type before ordering.

Documents and quotation

The official Caleffi 519 series datasheet 01007/22 EN (2022) is linked on this page. Send the code, quantity and pump data to request a quotation. See more in Hydraulic Valves & Components.