I have on old building with steam heat. Can I save on fuel by turning off the steam to the radiators in some?

Those valves are suppose to ‘spit’. They are pressure relief valves. Turning off any of the radiators won’t do anything for your heating bill. The boiler will still require the same fuel to keep everything else warm.

the more you turn off, the less the heater will run.

The more rooms you turn off the less the boiler will have to run. That will save you on your fuel bill. For more info, check out the hydronics page at my source.

your not going to save on gas necessarily because you shut down certain radiators you may just increase your fuel bill i found that when you shut down rads it creates a heat sink making the other radiators heat travel away and hot always goes to cold thermostat placement has a major role on how effective and how long your boiler will run steam is a very tricky heat medium it wont go where there is air hence the reason you have air vents on your rads as the steam enters a rad its has air in it the vents are designed to open when a radiator is cool allowing the incoming steam to purge out the air as the rad heats up the air vent closes some rads have steam traps which allow the condensated steam (water) escape back to the boiler without letting the steam escape clogged return pipes are a major cause of spitting air vents because the condensate isn’t getting back to the boiler fast enough …they have steam management systems that can save you money on a big building which is no more than a glorified t-stat

Your radiators are not suppose to spit anything. They will if you open the bleeder valve to purge them of air.
Your not going to gain anything by doing this. I removed two radiators from areas that didn’t need them, in the bathroom, it was so hot in there. And on in a hallway. It makes little difference.