<span style="font-family: trebuchet ms,geneva; font-size: medium;">For the "Monster Vac" competition when the club meeting took place here in Los Angeles, I did something similar with two Electrolux Model Ss. </span>
<span style="font-family: trebuchet ms,geneva; font-size: medium;">The results were disappointing -- there was no more suction with the two machines coupled together than each one singly. Something about how two motors of equal power canceled each other out, I was told. </span>
<span style="font-family: trebuchet ms,geneva; font-size: medium;">I wonder if having the "Y" connector further away from the machines, as with the Twin Filter Queen model, might make any difference. </span>
<span style="font-family: trebuchet ms,geneva; font-size: medium;">I also used a long 2"-diameter commercial-type hose connected to it, about 12 ft. long, and the Model XXX commercial-length floor brush (1.5x longer than the normal attachment). That may also have impacted the performance but I don't know.</span>
<span style="font-family: trebuchet ms,geneva; font-size: medium;">Member Michael Hays of Ohio has a central vacuum system with two motor units. I've never seen it but have heard that "it'll suck dry paint right off the wall!"
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