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5.4 Double Mechanical Seal.
This seal arrangement requires a supply of media to be circulated between the
inboard and outboard mechanical seals.
Q = (0.6 x p + 0.25) x n x d
3
x T
c
p
x ρ x 2.5x10
9
Q = Flow rate [ l/hr ]
p = Applied buffer / barrier pressure [ bar ]
n = Shaft speed [ rpm ]
d = Shaft diameter [ mm ]
T = Temperature of processed media [ °C ]
ρ = Specific gravity of buffer / barrier fluid [ kg/dm
3
]
c
p
= Specific heat capacity for buffer / barrier fluid [ kJ/(kg x K) ]
Typical values for some common barrier fluids:
Media Density [kg/dm
3
] Specific Heat [ kJ/(kg x K)
Water 1.0 4.2
Olive Oil 0.9 1.6
Mineral Oil 0.9 1.7
Acetone 0.8 2.2
The sealant system should be in operation 15 minutes before the product
pump is switched on, and 15 minutes after the product pump is switched off
The flow rate of the barrier fluid should be calculated to achieve the required
amount of heat removal per formula above. As a guide 2 to 3 litres/min for
Carbon v. St.St., Carbon v. SIC. 3 to 4 litres/min. for SiC v. SiC & TC v. SiC.
The barrier fluid should be clean and stable
Do not operate seal in product temperatures in excess of 248° F without
consulting Wright Flow applications engineering
The flush media must be supplied at a minimum flow rate of 0.5 Litres/ Minute
per seal, this can be worked out by the following equation where “Q” is the
flow rate.
5.5 Seal Pressure/Speed/Temperature Limits
Pressure and speed are two of the most important factors for frictional heat
generation in a mechanical seal and the seal face material properties set limits
to these parameters. Depending upon processed product properties, the
mechanical seal design and the seal face materials tribological, physical and
thermal properties the below specified limits can differ.
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