Weil-McLain 88 manual Piping multiple boilers, By-pass circulator sizing

Boiler manual: • Installation • Start-Up • Maintenance • Parts

Connect water boiler piping (continued)

Figure 16 Recommended minimum pipe sizes when flow rate is	Figure 18 By-pass piping for return water less than
not known (see Figure 14, page page 14) (note 1)		140°F

Boiler	Supply pipe size	Return pipe size
model	A	B
488	3"	3"
588 – 788	4"	4"
888 – 1188	5"	5"
1288 – 1888	6" (note 2)	6" (note 2)

Note 1 Pipe sizes are based on a 20°F temperature rise through the boiler. For applications with higher flow rates (lower temperature rise), determine the flow rate and use Figure 15, page page 14 to size the piping.

Note 2 6-inch piping requires nipples and 5" x 6" reducing couplings (provided with 1288 through 1888 boilers only). The total pressure drop through the 1888 boiler using the nipple and reducing coupling will not exceed ¼ PSI. For smaller boilers, the pressure drop will be less.

By-pass circulator sizing:

1.Size system circulator as required. Determine GPM and head requirements.

2.Provide a by-pass circulator for EACH boiler. The flow rate for each by-pass circulator will be:

Flow = ¼ x (System circulator GPM) ÷ (# of boilers)

Figure 17 ASME drain valve size

Boiler		Minimum blow-off
model		valve size
488	– 588	1"
688 – 1088		1¼"
1188	– 1888	1½"

Piping multiple boilers

1.See Figure 18. (Expansion tanks, relief valves and other accessories are required, but omitted from the illustration for simplicity.)

2.The boiler piping circuits are referred to as the secondary circuits in the following.

3.The legend for Figure 18 and boiler pump sizing recommenda- tions follow:

ASize boiler pump GPM based on the following:

a. Temp rise = High limit temp – Return water temp

b GPM. =	Boiler Gross Output, Btuh
	Temperature rise x 500

c.Calculate only secondary (boiler) piping circuit resistance. Al- low for head loss through the boiler equal to three 90 degree elbows of secondary pipe size.

d.Operate each boiler and its pump with a Weil-McLain boiler control panel.

e.Size secondary (boiler) circuit piping using the flow rate ranges given in Figure 17, page 15.

BPrimary pump GPM and head calculation should not include secondary boiler circuits. Primary pump can operate continuously during heating season.

CConnection to primary circuit — Space 12" maximum or as close as practical.

DCheck valve.

EHand valve.

Part No. 550-100-068/0308

3.All circulators must run at the same time.

4.Example: For a 1,000,000 Btuh single boiler, with system temperature drop of 20°F:

•System GPM = 1,000,000 ÷ 20 ÷ 500 = 100 GPM

•By-pass GPM = ¼ x 100 GPM = 25 GPM

•Determine by-pass circuit head loss for pipe size and fittings used.

5.In most applications, a standard booster pump should be adequate.

Figure 19 Multiple water boiler piping

15