System-Bypass Piping Method - Williamson-Thermoflo GWA 3 Series Manual

5 Water piping — multiple zones
Water piping — low temperature systems

SYSTEM-bypass piping method

This piping method (Figure 16) is called a system-bypass be-
cause part of the circulator flow bypasses the system (through
valve 7a). This bypassed hot water from the boiler outlet mixes
with cooler system return water temperature in order to pro-
vide minimum 130°F return water to the boiler. Valve 7b will
most often be full open, but may need to be slightly closed
on some low pressure drop systems in order to cause enough
flow through valve 7a.
Figure 16 is an alternative piping method that provides return
water temperature control for boilers installed on converted
gravity systems (large water content or steam systems).
DO NOT apply the piping of Figure 16 on radiant heating
systems. It provides no method of regulating the water tem-
perature provided to the system and could result in excessive
water temperature in the radiant tubing.
Figure 16
System-bypass piping — Zoning with zone
valve or circulators, return water 130°F or higher
— (Alternative to boiler-bypass piping Figures
14 and 15, page 18).
Failure to prevent low return water temperature to the boiler could cause corrosion of the boiler sections or
burners, resulting in severe personal injury, death or substantial property damage.
Radiant heating system piping should include a means of regulating the boiler return water temperature
and the system supply temperature (such as provided by an injection pumping control).
Boiler return water temperature will be adequately controlled using the methods shown in this manual pro-
vided the system supply temperature is relatively constant.
apply the methods of this manual if the system is equipped with an outdoor reset control. Instead,
DO NOT
provide controls and piping which can regulate the boiler return water temperature at no less than 130°F
regardless of system supply temperature. Contact your Williamson-Thermoflo representative for suggested
piping and control methods.
Failure to prevent cold return water temperature to the boiler could cause corrosion damage to the sections
or burners, resulting in possible severe personal injury, death or substantial property damage.
Part Number 550-142-320/0720
GWA Series 3 Gas-Fired Water Boilers – Boiler Manual
System-bypass piping as shown in Figure 16 can be used with
either zone valve or circulator zoning. When used with circulator
zoning however, the boiler circulator (item 3), must be piped
as shown. It cannot be used as one of the zoning circulators.
DO NOT apply system-bypass piping if the reduced flow in the
system could cause poor heat distribution. That is, system-
bypass piping reduces the flow in the system and increases
the water temperature supplied to the system. This can cause
increased heat from radiators at the beginning of the system
and reduced heat from radiators near the end of the system.
Valve adjustment
1. Start with valve 7a fully closed and 7b fully open.
2. Gradually open valve 7a while closing valve 7b until the
temperature at gauge 8 reads at least 130°F at all times.
3. Valve 7a regulates the amount of boiler supply water mixed
with return water. Valve 7b causes a pressure drop in the
system needed to balance flow through valve 7a and the
system.
4. The valve adjustment should be done with the system at the
coldest expected temperature (60°F for converted gravity
systems or high mass radiant systems).
LEGEND:
3 System or zone circulator
7 System temperature valves (see instructions to the left for
adjusting valves)
8 Blend temperature gauge
9 Relief valve
10 Automatic air vent (with diaphragm-type expansion tank),
or connect to tank fitting (closed-type expansion tank). DO
NOT use an automatic air vent when using closed-type ex-
pansion tank. It would allow air to leave the system, causing
waterlogging of the expansion tank.
11 Fill valve
12 Diaphragm-type or bladder-type expansion tank, if used
(For closed-type expansion tank, pipe from top of air sepa-
rator to tank fitting as in Figure 6, page 11.)
continued
continued
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