Weil-McLain 78 manual 5a Connect Water Boiler Piping, Installation, Start-Up, Maintenance, • Parts

• Installation • Start-Up • Maintenance • Parts

5a Connect Water Boiler Piping

General water piping information:

•System water supply and return piping should be installed and piping connections attached to boiler before erecting jacket or installing controls.

•Do not pipe in through supply and out through return. This creates reverse water flow through boiler that must not be used.

•When three-way valves are used for temperature modulation, install slow-opening (minimum 10-minute) valves and boiler mixing pump to minimize potential of boiler thermal shock. See W-M Bulletin AE-8402.

Install piping:

Install piping as shown in Figure 12 below for single boilers, page 14 for multiple boilers.

Improperly piped systems or undersized piping can contribute to erratic boiler operation and possible boiler or system damage.

1.Connect supply and return piping:

a.Size according to tables below.

1)For unknown flow rates, size piping per Table below, using 20°F. temperature

rise through boiler.		System
		supply
		(front only)
Cold	Expansion
	tank
water fill	Check
	valve
Manual		Water
		meter
isolation
valve	Pressure
	reducing
	valve	Manual
	(when used)
		isolation

valve

System return (front or rear)

Part No. 550-141-705

Figure 12 Water Boiler Piping

Recommended Minimum Pipe Sizes

for Unknown Flow Rates*

	Supply	Return
Boiler	Pipe Size	Pipe Size
Model	A	B
378	2"	2"
478	2-1/2"	2-1/2"
578-678	3"	3"
778-1278	4"	4"

*All piping sizes based on 20°F. temperature rise through boiler.

2)For known flow rates or higher flow rate through boiler, size piping per Table below.

Flow at higher velocities than shown in Table below for pipe size can damage boiler, causing substantial property damage.

Recommended Minimum Pipe Sizes

for Known Flow Rates

Water	Supply	Return
Flow Rate	Pipe Size	Pipe Size
GPM	A	B
Up to 35	2"	2"
36 to 50	2-1/2"	2-1/2"
51 to 77	3"	3"
78 to 142	4"	4"

b. Locate circulator in supply piping.

c. For return piping, use full diameter pipe for 10 times that diameter before making any reduction. For example, a 4-inch return should not be reduced any closer to boiler return tapping than 40 inches.

d. Install system blow-off (drain) valve in lowest part of return piping close to boiler. ASME Size requirements are shown in Table below.

ASME Drain Valve Size

Boiler Model	Valve Size (in.)
378-478	3/4
578-1178	1
1278	1-1/4

13