This sounds like what old Rolls Royces and some Jags have. The Rollers have two nitrogen (?) filled accumulators to keep a few pumps in reserve. Not sure about the Jags.
Pretty sure all the vacuum boosted cars I've owned had 2 or 3 pumps in reserve (unless they had a leak / bad check valve).
Jarrod.
“I offer my opponents a bargain: if they will stop telling lies about us, I will stop telling the truth about them”
― Adlai E. Stevenson II
