How Does The PSS Mechanical Shaft Seal Work?

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29 Νοε 2013 (πριν από 3 χρόνια και 10 μήνες)

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The

PSS

Shaft Seal

is the number one selling marine mechanical seal worldwide and is installed as standard equipment by many of the
worlds most reputable boat builders / yards. The

PSS

Shaft Seal is also recognized as the premiere retrofit (aftermarket)
seal on the
world market. Certified by Bureau Veritas,

ABS

& Rina: Boat builders / yards recognize the advantages and value of installing
the

PSS

as it eliminates the maintenance, constant adjustment & cost associated with traditional packing type glands.
Aside from these
benefits, the

PSS

Shaft Seal helps to eliminate water in the bilge (100% water tight) & wear to the propeller shaft. The

PSS

Shaft Seal
can be easily retrofitted and is available for shafts ranging from 3/4" (20mm) to 6" (150mm).

The

PSS

Shaft Seal

is a mechanical face seal that is created between the flat surfaces of the rotating stainless steel rotor and the
stationary carbon flange. The stationary carbon flange is attached to the vessels stern tube with hose clamps and the carbon
flange

is
attached to the front side of the bellows with hose clamps. The stainless steel rotor is fit on the shaft in front of the car
bon flange. The
stainless steel rotor is used to compress the bellows before the collar is secured to the shaft with set
-
screws
. This compression (pre
-
load) maintains contact between the faces and allows the

PSS

to compensate for the thrust from the propeller. The carbon flange is
bored larger than the shaft diameter allowing it to “float” around the shaft and thus compensate for
most misalignment and vibration
problems. The stainless steel collar is sealed to the shaft by two o
-
rings that are recessed into the bore of the collar. These o
-
rings rotate
with the shaft and stainless steel rotor and do not experience wear during operat
ion.

How Does The

PSS

Mechanical Shaft Seal Work?

A mechanical seal is created by the contact of a turning surface against a stationary surface. In the case of the

PSS
Shaft Seal, the
stationary surface is a carbon flange held in contact against a stainless

steel rotor which turns with the shaft. The carbon flange is
attached to the boat by a nitrile bellow which, with the help of water pressure, produces a constant contact between the carb
on and the
stainless steel ring. These type of seals are unaffected b
y engine motion or vibrations. The result is a 100% watertight and totally
maintenance
-
free seal.


Warning!

All mechanical seals look very similar. There is, however, a big difference in materials
uses in the components and subsequently in the way the seal
s will perform.

Materials Reference for the

PSS

Shaft Seal

1)

HIGH

DENSITY

CARBON
/
GRAPHITE

FLANGE

This space age composite is machined to shape. The face is then lapped to 4 light bands. Once installed and operational the
carbon/graphite face will actually

polish the stainless steel rotor face during the initial minutes of operation. This polishing process
ensures a perfect seal and eliminates the necessity of a spray guard. The high density of this composite greatly increases it
s impact and
wear resistance
. At a maximum operating temperature of 500° F, the carbon guards against any overheating situation unlike other seals
using plastic derivatives. The carbon/graphite flange should never need replacing under normal operation conditions.

2)

DOUBLE

O
-
RINGS

Th
e nitrile O
-
Rings are fit inside the stainless steel rotor to guarantee alignment and seal of the rotor to propeller shaft. Nitrile is th
e
material used due to its superior resistance to petroleum products, temperature variations and resistance to tearing.

These O
-
rings are
stationary and do not wear.

3)

STAINLESS

STEEL

ROTOR

The one
-
piece stainless steel (Type 316) rotor is slid down and secured to the propeller shaft with double set screws. Precision tole
rance
are maintained by computer controlled lathes.

After machining, the rotors are passivated to military specifications for maximum corrosion
resistance. The stainless steel rotor should never need replacing under normal operating conditions.

4)

DOUBLE

ALLEN

HEAD

SET

SCREWS

Allen head set screws with cup
ped ends (to prevent damage to shaft) are threaded into the rotor and secured to the propeller shaft. A
second set screw is then threaded into each hole to secure the first screw and to prevent it from possibly backing out. Set s
crews are
treated with a Dr
i
-
Loc 204.

5)

DOUBLE

HOSE

CLAMPS

Two stainless steel hose clamps are used to secure the bellow at both the stern tube and flange ends.

6)

BELLOW

Bellow is resistance to petroleum based products and set retention. It provides the best combination of durabil
ity, strength and elasticity.
The stern tube end of the bellow is available in 1/4" increments. Both shaft and stern tube diameters are necessary when orde
ring.