When I set up my vacuum pump (home made) I also bought a vacuum generator as well as a backup. In case your main pump fails you should have a backup "plumbed" and ready.
http://www.vacmotionorders.com/vcv10hs-basic-venturi-vacuum-generat.htmlWhile I have never had a problem, it's nice to know that I have a spare in the shop.
When I first started looking for my main pump last year I went to a dairy farmer friend that was just in the process of selling their farm.
I asked if they wanted to sell one of the pumps they use to milk the cows ( a roots vane type) but another farmer had taken them earlier in the week
