Looks like some old 1960s design.if you are going to design and build your own machine then start thinking out of the box,  this is (just like I said)  some old design.
The vacuum unit should have been designed to offer dry vaccing, then straight away it’s  2 machines in one, you don’t need to carry a separate vacuum on the van..... you can use the Tempest.
The pump unit needs auto fill and a pressure washing size pump,  then like the vacuum unit you have doubled the range of the machine. it’s not only a carpet cleaning machine but also a pressure washer ( perfect for car valeters who use both machines)
Unless these machines are significantly cheaper than a normal extractor why would you buy it?