Smoke pressurisation and fire door seals

[wee brian]

Sorry but you've lost me there.

As lin says you must have a leaky system or you will get equilibrium (which is no good)

[Thebeardedyorkshireman]

Agreed. Consider equilibrium. What causes 'the smoke to come through' when you have this state? By definition under the pressure laws, flow takes place from high to low, therefore if you have flow you cannot have equilibrium.
Before we go off on a new thread, I agree that you must have a leaky system.

[kurnal]

Having looked into this a bit further theres another couple of issues that other readers  have suggested to me   that support the absence of smoke seals.

One is that the system needs to be designed with a certain level of leakage as lin pointed out and it is important that tha design leakage paths are maintained. If there was too little leakage the fan would not have a consistent load and would be prone to overspeeding and motor problems

The other is that a consistent leakage path is important to the safe design of the system. If we used smoke seals their sealing ability is inconsistent as they wear out, thus potentially throwing the fan size calculations out as the system ages.
(thanks for that Andy) Hey Guys I'm converted- thanks. And wee B you are right once again. But I will win one one day....

[Martin Burford]

Kurnal

As always your postings are perceptive.  no to deal with leakage: For efficient and effective pressurisation there must be sufficient leakage through the external envelope of the building so that the pressure in the fire room cannot reach equilibrum with the protected volume[ stairs], say in this case. In buildings with airtight structures an automatic vent may be necessary. however most buildings are sufficiently leaky for this not to be necessary.

Yes many eventful nights I recall spent at UBB !!!.those were the days!!!

Conqueror.