Step 1 - preparation, For snap switch see step 3) – Xylem MM 711B Series 150, 150S, 157, 157S Bellows Replacement User Manual

Page 2

STEP 2 - Changing the Bellows for Mercury Switch Units

(For Snap Switch See STEP 3)

c. Make sure tapped hole on float arm (K) is facing the

correct way, so the float and float rod (C) can be
screwed into it when bellows assembly is assembled
on the head casting. Place gasket (M) on casting (B).
Center the gasket and place the bellows assembly (F)
and switch housing (A) on head casting (B). Insert and
tighten six (6) Torx

screws (E) to 125 in. lbs. (14 N•m).

d. Screw float and float rod (C) into float arm (K) and

hand tighten. Center the float rod in the float rod
guide (not shown) and tighten Torx screw (D) to
125 in. lbs. (14 N•m). Make sure you hold the float
in place while tightening screw (D). Move the float
up and down, making sure there is no binding and
that the float rod is still centered.

b. Take the new bellow assembly (F) and disassemble it

noting the order of the parts. Put sealing washer (J) on
top of float arm (K) and insert into inside of bellows (F).
Place gasket (L) over bellows (F). Insert this assembly
into switch housing (A) and bracket (H). If the screw (D)
was an Allen

screw, the spacer washer (G) will have to

be put in the top hole of bracket (H). Take Torx

screw (D)

(furnished) and insert it into hole on top of bracket (H) and
spacer washer (G) (if needed) and screw into float arm (K).
Hand tighten only.

a. NOTE: On units that have Allen

head screws they should

be replaced with Torx

screws (furnished).

Step 3 - Changing the Bellows for Snap Switch Units

a. Clean out sealant and remove two (2) screws (N)

and bracket (P). Remove (6) Allen

or Torx

screws

(E). Remove switch housing (A) from head casting (B).
The switch bracket (R) will come out with the switch
housing (A). The bellows assembly (F) may stick to
the switch housing (A). Remove bellow assembly (F)
and clean gasket surfaces on both head casting (B)
and switch housing (A).

OFF

a. To prevent electrical shock turn off all electrical

power to the boiler.
CAUTION: There may be more than one source
of power to the boiler.

STEP 1 - Preparation

b. Release all pressure from the boiler and let it cool down to 80˚F (27˚C). Drain the water level

down below the float chamber.

c. Remove the four screws that hold the cover on the

switch housing (A) and remove the cover. Mark all
electrical supply wires so they can be returned to
the proper terminals. Remove the wires and conduit
connections from switch housing (A).

d. Remove eight hex head bolts holding head

mechanism (B) to float chamber. Carefully remove
head mechanism (B) from float chamber and place
in a vise.

e. Holding float (C) firmly, unscrew Allen

or Torx

fastener (D). (Units with date codes of E99 or earlier
will have Allen

head fasteners. Those with codes of

F99 or later will have Torx

fastener). Unscrew float

and float rod (C). For snap switch units see Step 3a.
For mercury switch units remove the two mercury
switches. Remove six (6) Allen

or Torx

screws (E).

f. Remove switch housing (A) from head casting (B).

The bellows assembly (F) may stick to the switch
housing (A). Remove bellow assembly (F) and
clean gasket surfaces on both head casting (B) and
switch housing (A).

Four Cover
Screws

Eight Hex
Head Bolts