I bought one of those blowers that Andy LaTorre wrote about.  I haven't
used it yet, but I had planned to use it with a 24-note rank of pipes
that would be voiced to play at very low pressure (around 2 inches).
If one needs more air volume a second blower could be added as they are
quite compact.  For the money, it's worth a try.

On an O roll, I don't think any more than two or three pipes are played
at the same time, more like one or two pipes.  I think the blower could
handle that if it has the static pressure that Andy mentioned.

Wade Newton