Drayton Automatic By-pass Valve

Building Regulations

An Automatic Bypass valve (ABV) controls water flow in the Heating Circuit according to the water pressure across it and is used to maintain a minimum flow rate through the boiler and to limit circulation pressure when other water path's are closed. A bypass circuit must be installed if the Boiler manufacturer requires one, or specifies that a minimum flow rate has to be maintained whilst the boiler is firing.

The use of Automatic Bypass Valves becomes particularly important when heating systems include large numbers of Thermostatic Radiator Valves (TRVs). Whilst the TRVs are open, the Automatic Bypass Valve remains closed. However, as the TRVs start to close, the Automatic Bypass Valve starts to open, maintaining the required water flow through the boiler. Using an Automatic Bypass Valve is also likely to reduce noise in systems caused by excess water velocities.

Because manual or fixed position valves do not regulate the flow and allow water to bypass even when it is not necessary, Building Regulations require bypass circuits to use Automatic Bypass Valves and not fixed position valves.

Location in System

System with stored hot water

[Diagram Description: A schematic shows a heating system with a hot water tank, boiler, pump, 3-port valve, radiators controlled by TRVs, and an Automatic Bypass Valve. The bypass valve is installed between the boiler's flow and return pipes. An arrow indicates the direction of flow through the bypass valve. The system includes labels for Tank, Boiler, Pump, Radiators, TRV, 3 port valve, and Auto Bypass Valve.]

System with combi boiler

[Diagram Description: A schematic shows a heating system with a combi boiler, pump, radiators controlled by TRVs, and an Automatic Bypass Valve. The bypass valve is installed between the boiler's flow and return pipes. An arrow indicates the direction of flow through the bypass valve. The system includes labels for Boiler, Pump, Radiators, TRV, and Auto Bypass Valve.]

The by-pass should be installed between the flow and return with flow in the direction of the arrow. If a higher capacity is required for large installations, it is possible to install two or more valves in parallel.

Installation Steps:

• Install the ABV so that the flow direction is in line with the arrow on the body.
• Fully engage pipework into the body and screw the compression fitting until finger tight.
• Use a correctly sized open-ended spanner to tighten. Do not over tighten.

Setting Procedure

1. Commission and balance the Heating System - take note of the selected pump speed.
2. Using the Boiler manufacturer's instruction, find the minimum flow requirement for the Boiler.
3. Using the Pump manufacturer's Pump curves, determine the available Pump head when operating at the required minimum flow and the selected Pump speed.
4. Using the Setting chart, the calculated Pump Head and the minimum Boiler Flow, find the optimum setting for the ABV.

Example:

Minimum flow 300 l/h - Pump speed 3. Pump chart indicates 4m head (Use Pump Manufacturers chart). Pump head. 1m = 100 mbars.

[Diagram Description: A graph shows Pump Head (in meters) on the Y-axis and Flow (l/h) on the X-axis. Several curves represent different Pump Speeds (1, 2, 3). The example highlights finding the available head for a specific flow rate.]

[Diagram Description: A setting chart example. The left chart shows Minimum Boiler Flow (l/h) on the X-axis and Pressure Drop (mbar) on the Y-axis, with lines indicating ABV settings (0.1 to 0.5 bar). The right chart illustrates how to use the setting chart: given an example of 4m head and a minimum flow of 300 l/h, the result is to set the ABV to 0.40 bar. This involves finding the intersection of the minimum flow line and the pump head curve on a separate chart (not fully detailed here but implied by the example text) and then using that point on the ABV setting chart.]

Note: To set the ABV, turn the red setting cap until the white pointer corresponds with the required setting (in bar). Should persistent water velocity noise occur in the Heating System, gradually turn the ABV to a lower setting until the noise is eliminated.

Features

• Maintains optimum flow
• Automatic operation
• Set and forget
• Ensures quiet operation
• High quality
• Reliable

Technical data