With most things, maintenance is designed to save you money; however plumbing maintenance can be one of the most draining ventures that you could possibly consider. Plumbing, be it domestic or commercial, has so many variables that maintenance thereof could often cost more than the installation itself.
This is why most people do not subscribe to plumbing maintenance theory, using the logic that they are going to screw you over anyway, so you may as well wait for something to go wrong. Of course in the case of commercial plumbing, people do not have the luxury of waiting for something to break, because in the case of a restaurant or factory a burst pipe can cause large sums of money to be lost (and in the case of restaurants they might never get it back).
The industrial sector has made many a plumber a rich man. The maintenance contract for a large factory could be worth millions to whoever holds it. Health and safety regulations means that they have all systems checked regularly, this is especially the case with valves that are carrying large amounts of pressure. The problem that the factory owner faces is that chances are he/she does not know all that much about plumbing. So when the plumber comes to do a routine maintenance check, they are completely at his/her mercy.
They have to take his /her word, and what an expensive word that can be. The maintenance guys put the fear of God into business owners by emphasising the possible dangers of not replacing a valve. They talk about lives that are at risk and possible lawsuits. Many of them are so good that you end you are handing over a blank cheque. This is why so many companies employ in house plumbers.
Restaurants and bars face similar problems. Lucky for them plumbing maintenance is not mandatory, but this does not mean that they are off the hook. Most managers have to double up as maintenance staff but this only works for minor plumbing problems.