I thought after they had gone below a certain psi you were,nt supposed to reinflate them? Health and safety and all that. Could be wrong I just remember someone mentioning it.
A lot of the garage forecourt airlines are ‘turned down’ for Health and Safety reason, no garage owner wants the responsibility of wiping a driver up after his punctured tyre that has weakened blows up in his face… 
Have always used bigger tyre dealers. Never a problem. Sometimes a couple of quid helps.
OR
Call in a haulage yard - if no air you may get a cuppa and the pzss taken 
the only garage i know that has the capability of blowing up tyres to their correct pressure when out on the road is purdy lodge(in my area i work).not one msa im aware of is capable of blowing tyres up to 120 psi.the only down side to purdy lodge is the lead is quite short and to check tyres on the other side you have to turn the truck.also it is just about on one of the pumps,so mayhem can and does ensue,but it is free.most msa"s dont have a big enough compressor to allow trucks tyres to be correctly inflated.hazarding a guess i would say its the same size compressor as the car inflator,and they have the audacity to charge?.tbh why do they bother installing them if they are not fit for purpose?,as i suspect,another way of fleecing the public.
I’ve got airline allways with me , just in case and i’m using it from time to time.
free air is at Shell garages :
- A63 melton just few miles from hull westbound.
- A63 brough just off the M62 eastbound
- M1 close to J28 southbound and northbound at MSA.
- M62 close to J26 westbound at MSA and not for sure is the same at eastbound.