Poseidon xtream set up

[Frogman82]

After adjusting the IP on full tank pressure, can the cracking pressure be fine tuned on a partially used tank?

 

[tbone1004]

the first stages are not perfectly balanced and since the second stage is an upstream valve you want to tune it at the lowest IP it will experience which needs to be with a full tank. If you fine tune it at anything less than a full tank it will leak when you put it on a full tank. The MK3's are better balanced than the older designs but still aren't perfect.

 

[Frogman82]

Thanks @tbone1004!

 

[p_kos]

the first stages are not perfectly balanced and since the second stage is an upstream valve you want to tune it at the lowest IP it will experience which needs to be with a full tank. If you fine tune it at anything less than a full tank it will leak when you put it on a full tank. The MK3's are better balanced than the older designs but still aren't perfect.

How “not perfectly balanced” do you find 3960s? Mine seem to swing 8-11psi.

 

[tbone1004]

How “not perfectly balanced” do you find 3960s? Mine seem to swing 8-11psi.

mine swing about that much, more than enough that it's critical to check them at the extreme's. I tune all of my Jetstream/Xstreams at 4000psi, and Cyklons at about 300psi

 

[rsingler]

You can improve the balance in a couple of ways. First, replace the bias spring (#1180). Next, put a second Teflon washer (#2822) behind the bias spring. You'll be surprised.

The same thing works for the Xstream. First try replacing the bias spring (#4555). Next, add a 2-006 PTFE backup washer (like a Conshelf) down in the pocket in the reg body under the ruby ball bias spring (#4555).

You can increase the reg's stability to the point of making it like a piston regulator (increasing IP with increasing tank pressure), depending upon the extent to which you shim the bias spring.

 

[Frogman82]

Okay, so I built myself a diy magnehelic gauge with the u-tube of water. Adjusted the regs to 28 mm wc as stated in the manual. But then I tested the cracking pressure on both an analog magnehelic and a digital one and both give a cracking pressure of 50 ish mm wc. The one I built still reads 28-30 mm wc. My understanding was that the water filled tube was the most accurate one. The hose on the analog gauge is quite a bit thinner than the 1/4 inch I used on the one I made, but does that really matter?

 

[rsingler]

Try vodka to decrease the surface tension in the liquid manometer. Mine is within 3mm of my magnehelic.
And I hate to bring it up, but did you remember to measure not just the rise in the water column, but the difference between the rise in one arm, and the drop on the other side? 28 x 2 is a lot closer to 50.

 

[Frogman82]

No I actually thought it was only the rise of the water that was measured, not the drop in the opposite tube also. So you basically have to add the two to get the correct reading?

Edit: I realized that my understanding of the u-tube manometer was wrong. I thought it was just the rise of the water that was measured and this is why the reading on the magnehelic is different.

 

[Frogman82]

In my quest to tune the xstream as good as possible I have a couple of questions.
Using a water filled tub as per the field service guide it says that «A sizzling sound from the servo-valve opening shall occur within the two markings.» Is this sizzling sound the servo trickle or the main valve opening?
Using a magnehelic gauge, is the cracking pressure 1,1-1,4in when the servo starts to trickle or when the actual valve opens as normal for the cracking pressure?