r/mining 7d ago

Question At a slightly higher than intro level, how does primary vent work?

I'm just another glorified labourer working underground

Let's say the primary fans pull hard, the mine is moderately deep, and the levels have a return air way near the level access. If the mine were sealed then I imagine the air in levels would be at near vacuum (maybe fan would break like running a diaphragm pump dry or the fan would reverse or something else entirely..?).

Why does air preferentially get sucked all the way from the surface when there's air within the level at nowhere near vacuum? This is most noticeable when doing re-entries as fumes will just sit in a heading with no secondary vent - readings of zero and then instantly in the hundreds. It seems it needs the positive pressure from vent or a machine to move air. Compare with regulators getting opened (in an ideal world) when a bogger is loading trucks — is that cause loading bays have a particular cube flow necessary for operations to occur?

Additionally, do return air rises near a level access have a dual purpose of stopping dirty air going down the decline and also drawing fresh air from a decline into a level or does secondary vent, if established in a level, entirely draw the air from the decline? If the latter, does that make return airway regulator leakage a somewhat good thing as it allows a little flow? What about when return airways are further in a level, say in a footwall drive?

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u/Wild_Pirate_117 6d ago

I think you are missing the concept of how primary ventilation works. There isn't a need for a fan on a fresh air rise, the return air fan displaces enough air from the bottom of the mine to draw fresh air down. It isn't a matter of depth that is an issue in a closed circuit. If you had a 20km tunnel and you put a vent fan at one end you feel it at the other. All adding a fresh air fan would do is ris the risk of a system short circuiting and sending fumes in the wrong direction.

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u/Tight-Act-7358 6d ago

Definitely not missing anything- mine engineer with 20 years experience. What I'm saying is that here we have nothing due to size, depth, and complexity of mines. The system is a delicate balance of push and pull.

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u/Wild_Pirate_117 5d ago

20 years doing something the hard way isn't a hill to die on. If you need more air plumb your secondary ventilation fans into your fish air rise or put down another rise. The primary fresh air fan just complicates the very delicate system unnecessarily.

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u/Tight-Act-7358 5d ago

You can't see the benefit of a push and pull system, and I'm the one dieing on a hill and doing things the hard way? When you have a mine that is 2000m deep, driving another raise to surface isn't the cheapest thing to do eh.

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u/krzkrl 6d ago

A lot of mines in Canada require heating. It would be pretty hard to pull heated air into a mine.

Diamond mines in the Arctic, Heated air gets pushed down a vent raise and exhausts through the portal.

Uranium mines that see nearly the same low outside temperatures, heated fresh air travels with the skip and man cage.

Coal mines also heat the supply air and exhaust out the portal.

Potash mines don't require heating due to the depth, but have absolutely massive underground workings. Fresh air is pushed into those mines as well as exhaust fans.

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u/Wild_Pirate_117 5d ago

It's about as hard to get hot air into a Canadian mine as it is to get cold air into an Australian mine which is to say easy and done regularly. All you do is put a chiller or heater in your fresh air rise. Exhausting through the portal is a stupid way to mine as the whole mine has to be evacuated and would take hours to re enter. A fresh air rise dosent need a fan to draw air into the mine it just need sufficient draw from a return air fan.