12
Operation and Maintenance Manual
QC Series Centrifugal Pump
QC-M02
4. ASSEMBLING AND INSTALLING THE MECHANICAL SEAL
MECHANICAL SEALS.
Among the QC, QC plus, and IC plus pump series there exist five
types of mechanical seals.
One of these, the “
T21
”, is used exclusively with our IC+ series, specifically in non-sanitary
applications. As for the remaining four types, their selection must be based upon the particular
application and the properties of the fluid being pumped.
The “
D
” seal is the most common mechanical seal. It is used when the fluid which is going to be
pumped is neither corrosive nor abrasive. It is a balanced, external seal, designed to be long-
lasting.
The “
F
” seal is exactly the same as the “
D
” seal, but contains a water-cascade assembly to
lubricate and cool the seal. The water-cascade assembly is located on one side of the adapter.
This seal, although it is sanitary, is very dirty because the coolant tends to drip.
The “
DG
” seal consists of two parts: one stationary and other rotating. The rotating part consists
of the same elements as the “
D
” seal. The stationary part consists of one piece which may
be carbon silicone, ceramic, or carbon tungsten, and which is placed in a gland ring. This
type of seal is used when the fluid to be pumped is abrasive, corrosive, or contains a product
which impedes the seal lubrication. The stationary seal is made of a very strong material and is
reversible, so flipping the seal is sufficient to continue using it. The “
E
” seal is a double-balanced
seal cooled by water. This seal is composed of a stuffing box which is filled with fluid (normally
water) to cool the mechanical seal. The “
E
” seal is used in conditions similar to those of the “
DG
”
seal but in applications that handle extremely high temperatures (up to 500º F). It can also be
used in applications where there exists a vacuum of up to 28 in. of mercury.
EXTERNAL-BALANCED SEAL TYPES “D” AND “F”.
Locate the following pieces: carbon
(
80
), o-ring (
80B
), “D” seal cup (
80A
). “D” seal spring (
80C
), “D” seal drive collar (
80L
), set
screws (
80K
), and “D” seal backplate (
11
). Pre-assemble the set screws, making sure they do
not penetrate the inner diameter of the stub shaft and set the o-ring into the carbon so that it
sits at the back. Next, place the o-ring and carbon together onto the cup so that the cup’s three
legs align with the carbon’s slots. Then, fit the spring onto the cup so that the tip of the spring is
touching a fourth, folded leg on the cup. If necessary rotate the spring to touch the two pieces.
When handling the carbon (
80
), be careful not to bump or scratch the seat of the seal, as this is
the face that makes the seal.
For best assembly, the drive collar has a pin or key that
should fit into a slot in the cup. Use pressure to insert
the drive collar, making sure that the pin aligns with the
slot as shown in
Figure C.
Slide the entire assembly onto the stub shaft.
The o-ring seals the flow of fluid between the pump and
the exterior through the mechanical seal by filling the
space between the stub shaft and carbon.
ASSEMBL
Y