JEScholz
Contributor
What is the difference between Upstream and Downstream regulators?
Upstream or Downstream
- Thread starter JEScholz
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A downstream design uses a poppet that will open to vent excess intermediate air pressure. An upstream design will not vent this excess pressure and some other form of over pressure relief must be used.
In practice, if the first stage high pressure seat fails, the first stage intermediate pressure will rise and could cause a failure of the low pressure hose leading to the second stage unless the excess pressure vents through a downstream second stage or an over pressure relief valve.
Becuase of this threat, the term normally is applied to second stages although there are also up and downstream first stages. In fact all diaphragm first stages use an upstream design where the seat carrier is located on the upstream side of the high pressure orifice in the first stage. But it does not really matter as if the poppet fails closed, the pressure will still be contained by the regulator as it is rated to greater than the full tank pressure anyway.
In practice, if the first stage high pressure seat fails, the first stage intermediate pressure will rise and could cause a failure of the low pressure hose leading to the second stage unless the excess pressure vents through a downstream second stage or an over pressure relief valve.
Becuase of this threat, the term normally is applied to second stages although there are also up and downstream first stages. In fact all diaphragm first stages use an upstream design where the seat carrier is located on the upstream side of the high pressure orifice in the first stage. But it does not really matter as if the poppet fails closed, the pressure will still be contained by the regulator as it is rated to greater than the full tank pressure anyway.
Think of a door at the end of a corridor and compare that to the valve in your second stage at the end of your regulator hose.
If the wind blows the door open, it is like a downstream valve.
If the wind blows the door shut, it is like an upstream valve.
If the wind blows the door open, it is like a downstream valve.
If the wind blows the door shut, it is like an upstream valve.
Ed Palma
Contributor
Hello DA!
I was just wondering about what you said about 1st stage diaphragms. Is the default position of the HP seat on the crown open or closed? I mean, does the diaphragm spring on the LP side keep the seat open, or do the springs in the HP side keep it closed?
Also, would a failure of this upstream system lead to a rapid OOA situation? and what would be the conditions for this to occur?
Thanks!
I was just wondering about what you said about 1st stage diaphragms. Is the default position of the HP seat on the crown open or closed? I mean, does the diaphragm spring on the LP side keep the seat open, or do the springs in the HP side keep it closed?
Also, would a failure of this upstream system lead to a rapid OOA situation? and what would be the conditions for this to occur?
Thanks!
In a piston or diaphragm fist stage design, the mainspring lifts the seat off the orifice until adequate pressure builds up in the intermediate sections of the first stage to close it. So in a depressurized situation, the spring will keep the seat off the orifice in both designs.
If the mainspring breaks in either design you are basically screwed as the reg will probably stop delivering air, although there is a slightly greater chance that a piston design might continue to deliver air given the down stream design. Fortunately, mainspring breakage in either design is all but unheard of.
If the mainspring breaks in either design you are basically screwed as the reg will probably stop delivering air, although there is a slightly greater chance that a piston design might continue to deliver air given the down stream design. Fortunately, mainspring breakage in either design is all but unheard of.
Ed Palma
Contributor
Oh, okay. So for 1st stages, the risk of getting deep witness marks on the HP seat would be minimal with prolonged storage as oppoosed to the LP seats in 2nd stages which are held shut. So, if I wanted to store my regulators, would it be best to keep the purge buttin depressed in order to avoid sticky seats?
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