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No safety relief valves on low pressure network

simonverville Member Posts: 8
edited June 2022 in Strictly Steam
I have recently seen low pressure steam networks coming from high pressure district network without any safety relief valves. These are relativly old network (before 1960)

So, High pressure steam (>120psig) is coming in, reduced by PRV's and then distributed to the building(s) between 10-15psig. There are no safety relief valves at all.

I am wandering if those networks could have been designed for high-pressure even if they are intented to work at low pressure, so no safety's would be required?
I did not see anything that would suggest any safety's have been installed in the past.
Otherwise I don't see how it would be code compliant.

Anyone could tell me if that was comon back in the days


    EBEBRATT-Ed Member Posts: 13,790
    No. Not common at all and should be fixed immediately by installing the correct size safety valve(s).

    It's very common for PRVs to fail and leak by. They usually fail to hold set pressure and start to creep upwards on the outlet pressure.

    I am very surprised there is no safety valve installed.
  • retiredguy
    retiredguy Member Posts: 797
    I have never seen this type of installation anywhere but every state has some of it's own safety standards and system pressure codes that have changed over the years. That said, the only way I believe this could be acceptable would be if every device downstream of the boiler was pressure rated at a pressure the same as, or higher than, the boiler's maximum pressure. I would call my "state" and "insurance inspector", sometimes they are the same person, and ask them that same question. These are the people that should have all the answers.
  • pecmsg
    pecmsg Member Posts: 4,188
    I believe the PRV has the safety device. Our building had 2 safety's on the incoming main piped outside!
  • jumper
    jumper Member Posts: 2,121
    A mix up? Low pressure needs no relief when it's from a low pressure boiler that does have safety. A proper pressure reducing station is more than a regulated valve & drip.
  • simonverville
    simonverville Member Posts: 8
    @jumper I am talking about a low pressure network that is fed by high pressure boilers through PRV's, with no safety's downstream the PRV's.
    I am wandering if it could be possible that the entire low pressure network is rated for high pressure. Was this something common in the past?
    EBEBRATT-Ed Member Posts: 13,790
    edited June 2022
    No. That would not be common and is unlikely.

    Every district steam system requires safety valve(s) installed downstream of any PRV especially with a 120 psi supply.

    See page 20-21 in the attached

    To answer your question high pressure steam is used for distribution. For a heating system high pressure would be difficult to control. So they reduce it to low pressure. That is usually what is done. High pressure steam is also noisy. What kind of building is this? An old factory converted to condo's??

    That is NOT to say high pressure is never used for the final heat source. It is in sterilization, laundries, kitchens etc. And you can find some steam unit heaters and process equipment using HP steam.

    But for general steam heating systems no,

    Checking the pressure rating of the steam traps installed downstream of the PRVs. That will probably lead you in one direction.
  • simonverville
    simonverville Member Posts: 8
    @EBEBRATT-Ed I agree with what you are saying. However, I don't think the netwwork was meant to work at I pressure. I am just saying that MAYBE the components were rated for high pressure even if they actually works at low pressure.
    That is the only logical explaination I see to not having a a safety downstream the PRV.
    They are not building that have been converted. I can confirm that it has been designed like this from construction. I am just not sure if there was some safety's in the past that could have been removed years ago. But I don't see who would have taken this bad decision.
    I will check the steam trap rating. Good advice.
    EBEBRATT-Ed Member Posts: 13,790

    Check the piping diagram in the Sarco book I attached. Page 21. See if there are any plugged tapping's downstream of the PRV. If there was a safety valve and it was removed it probably would be within 10-15 feet of the PRV.

    If the steam traps are low pressure 15psi rated traps then for sure a safety valve should be installed
  • simonverville
    simonverville Member Posts: 8
    @EBEBRATT-Ed I found a part an answer in ASME B31.1. Looks like there are 2 Alternative systems for steam distribution system below 400psig (which is my case). One of my building was designed like option (A). See attached file.

    That explain why I did not see any safety valves
    ASME.JPG 268.4K
    EBEBRATT-Ed Member Posts: 13,790
    If you have two PRVs in series apparently that is ok. But I still think a safety valve is a better choice
  • dopey27177
    dopey27177 Member Posts: 887
    It is not a common practice to not have safety valves on low pressure steam systems. Often some of these buildings when retrofitted did not install safety valves because the discharge piping was piped to an unsafe location outside the building.

    The next safety set up is electrical protect on the pressure reducing valves.

    Again code compliance is paramont.