garage door opener

[fredhargis]

What I don't understand is how the door closes with a jack shaft opener. It seems the door would have to close by gravity since the opener (I guess) can't force it down. That seems to me like it would require a really well balanced door.

[jteneyck]

What I don't understand is how the door closes with a jack shaft opener. It seems the door would have to close by gravity since the opener (I guess) can't force it down. That seems to me like it would require a really well balanced door.

What's your logic for saying that, Fred?  If the opener can open the door, it should be able to close it under power, too, no?

John

[Roly]

What's your logic for saying that, Fred?  If the opener can open the door, it should be able to close it under power, too, no?

John

Dont they work by pulling the cables up to open the door ? If the door is open all the way there would be very little weight, if any to pull the door down.  They make pusher springs to start the door down then the opener can lower it. .  But what holds the door down other than weight to lock it ?  Roly

[fredhargis]

What's your logic for saying that, Fred?  If the opener can open the door, it should be able to close it under power, too, no?

John

I'm thinking of how a jack shaft opener opens the door, it pulls the door up by the cables (?). So now that it's up, it can't (I don't think) use those same cables to push the door down. Maybe I misunderstand the whole thing, or what Roly mentioned is the solution...pusher springs of some kind. It's not something I'll ever buy, but I am curious about how it works.

[JosephP]

A jackshaft opener simply turns the shaft that the torsion spring is connected to.

Whether you pull on the top of the door, push on the bottom of the door, or turn that shaft the springs in cables are assisting the lift.

Just like a traditional opener, when the door is going down, gravity would finish closing it without the opener in place. The springs would control that descent. They also limit how strong the gravity of the door is pulling on the opener.

[fredhargis]

But with the door fully open, wouldn't something have to get it down to about the 1/2 way point for it to close?

[Stwood_]

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[JosephP]

But with the door fully open, wouldn't something have to get it down to about the 1/2 way point for it to close?

Just like any other opener...or manually closing the door.

Instead of pushing on the top of the door, it turns the shaft.  By pushing on the top of the door, a traditional opener is also causing the shaft to turn.  If you didn't have an opener, you pull on a string on the bottom of the door - which also causes the shaft to turn.

[fredhargis]

Well, I still don't get it and I'm apparently not explaining myself very clearly. But I do thank everyone for trying to make me a little smarter, I do appreciate it. Like I said I'm not considering one so it's not really all that important. Seriously, thanks to all!

[jteneyck]

Well, I still don't get it and I'm apparently not explaining myself very clearly. But I do thank everyone for trying to make me a little smarter, I do appreciate it. Like I said I'm not considering one so it's not really all that important. Seriously, thanks to all!

Let me try it this way, Fred.  With my current chain drive, it pulls the door up to open.  To close, it reverses and pulls the door down.  Ideally, the torsion springs are wound so that the door has almost zero gravity.  It is held closed by the force of the chain pulling the door down.  

The jackshaft opener operates the same way, but instead of being connected to the top of the door like my chain drive system is, it's connected directly to the shaft with the torsion springs.  The opener drives the shaft to pull the door up, and reverses to pull the door down.  The torsion springs transmit their torque to the cables that do the work.  There's no difference between how it works regardless of the type of opener used.  

John