If question does not refer to ASME I'll give you my 2 cents.
PRV in LPG tanks are usually checked for set pressure during periodical hydrotest test of tanks.
This check is always done with water but procedure differs with operators.
You can test PRV on the tank fixing seat valve during hydrotest with a fastener and after then bringing down pressure on tank below set pressure, removing fastener and testing PRV increasing pressure again. This must be after hydrotest to avoid permanent fixing of valve seat.
You can test PRV on the tank too but threading to tank a gear consisting in a tube and a valve with a manometer in it.
Another way is putting PRV in this gear but connecting it directly to pump instead of threading it to tank.
In the two firts systems, as tank volume is big pressure goes up and down smooth but test fluid is always water. In third case gear volume is small and pressure lift fast and pulsating but if gear is empty full of air or you can empty it with drain valves you can test PRV with air using a water pump and pressure goes up slower.
Most LPG tanks cannot be filled with water because of the weight. I've never seen a LPG tank hydrotested unless it was repair on site. A lot of LPG tank vendors used an internal relief valve. The only wat to test and inspect the valve was to completely remove the tank from service and empty it. Some better manufacturers had a 100% redunrant PRV with a "Y" fitting and a valve under each PRV.
If you wanted to place a block valve under your PRV and install a test ring (a thick block that fits between the valve and PRV and has a 1/2" test port valve) you could do a lifting test in service. Normally, I've always taken the PRV off and had the who valve inspected to see if there is any mechanical problems. This is done on site with a company that has an ASME code shop and a portable shop.
I normally do this every 5 years, unless there was something to trigger an early inspection.
dcasto
May be you haven't seen a LPG tank hydrotested. I've seen hundreds instead. Most of them of less than 10 m3 in residential use.
All LPG tanks in spain are tested every ten or 12 years. Even big tanks in filling plants for road tanks are filled with water. Sometimes for thickness meassurements a boat is used while filling or emptying tank. Tests for this big ones include checks for changes in supports caused by weight.
As you said, "Y" fittings for two, three or more valves are used for bigger tanks than residential use and are usefull for testing or change valves with in service tank.
If I recall correctly, as I dont have my NFPA with me, being out of the country for a while,I think testing is recommended every ten years but how is the test to be done is not spelled out and that is the reason for my question.
The hydrolift test that I mentioned is a hydraulic oil test requiring oil pump, manifold, regulator and flex piping. Such test does not require removal of the safety valves while the boilers are opened for inspection ,therefore can propane PRV's be tested in a similar fashion or are their design preventing such test?
Now it's clearer. As you told, that's the way PSV in steam boilers are tested.
Applying a force in the sharf to set pressure and knowing force, actual pressure and surface of seat valve you may calc set pressure.
But PSV for GLP usually are internal or external Rego type valves with no shaft.
where are you going to apply force?
