I have another option to offer. I
purchased a Fein shop vac which Museum Services then retrofitted with the 10 amp
controller Peter mentioned in his email. When the controller burned out, I
had to replace it at my own expense, buying the part from Grainger. After
it burned out a second time shortly afterward I gave up and contacted an
electrical engineer. He told me that the 10 amp controller is too close to
the 9.something draw of the Fein vac and this is why it burned out - it is too
small (so would it be big enough for a Nilfisk?). He suggested I buy a
used "variac" on ebay - it's a powerful controller that you plug the vacuum
into. I did this, and it works beautifully. The drawback is that
it's somewhat big and heavy which limits your mobility. But you can plug
any vacuum into it and it really works. I have since purchased a Nilfisk
which has one great advantage because it is so quiet. But if the
controller goes I'll be using the variac with it.