Been in business 21 years and used a 135 psi for the first 19 of them, got a new machine with a 250 psi, 2 years back. and wish i never did, why? cos I should have got a bigger pump years back. yes a 135 does the job, but a bigger pump does it better and quicker. cleaning a nice carpet it makes no difference, but when it comes to removing lots of dirt you need power, think about it it makes pure sense, its only down side is money and weight