Subjective evaluation of G250V vs. D400 vs Air1 (in Pilot case)

[elan]

I have finally had an opportunity to have all 3 together on one dive today.

We had:
A G250V mounted on an MK17 ( IP @ 145)
A D400 mounted on a last generation MK20 with a composite piston (IP @ 130)
An Air 1 in Pilot case mounted on an MK5 (IP @ 125)



My friend's G250V was brand new on it's 5th dive, breathed as well as my G250Vs that is smoothly and very well. D400 was breathing noticeable easier. Air 1 blew away all the other guys, with no doubts.

I kind of understand that D400 is supposed to be an easy breather which it is due to the design and smaller case geometry fault and lower cranking pressure. But should the Air one breath even easier ? If so why ? Is it due to the location of the diaphragm ?

Given the IP values and the versions of the 1st stages I cannot contribute that to the flow rates and the IP of the 1st stages

 

[DA Aquamaster]

Subjectively speaking, you probably notice the larger area of the exhaust "valve" on the Air 1. Inhalation wise the D400 and Air 1 are probably pretty close.

I concur with your views on the D400 versus the GF250V, but the G250V produces better WOB numbers than the D400. I think that serves as an excellent example of how WOB numbers are a) flawed and 2) manipulate and used by reg manufacturers to sell regs. You can play with the inhalation and exhalation performance to reduce the overall work of breathing but in the process you can create a very unnaturally breathing regulator that does no "feel" good at all to the diver.

 

[elan]

May be my D400 is undertuned as I feel quite a difference with Air1.

I have another D400 that I would try to tune to and see if I can tune it to the performance of the Air 1.

I found this whole WOB business is a bit confusing.

Subjectively speaking, you probably notice the larger area of the exhaust "valve" on the Air 1. Inhalation wise the D400 and Air 1 are probably pretty close.

I concur with your views on the D400 versus the GF250V, but the G250V produces better WOB numbers than the D400. I think that serves as an excellent example of how WOB numbers are a) flawed and 2) manipulate and used by reg manufacturers to sell regs. You can play with the inhalation and exhalation performance to reduce the overall work of breathing but in the process you can create a very unnaturally breathing regulator that does no "feel" good at all to the diver.

 

[DA Aquamaster]

All D400s are not created equal. The early D400s with the one piece all metal aspirator/metal orifice and the single flat lever are very nice, very easy to tune and can produce a lower inhalation effort than the later two piece/plastic orifice aspirator and two flat levered D400s.

I suspect the change in the lever was related to CE freeflow requirements, although it was marketed as increasing the working range of the valve. The CE freeflow requirements were not kind to the D400 - or any other good breathing regulator, and I always got the impression that particularly silly requirement was intended to level the playuing field for lesser performing European models.

The later D400 poppets are also difficult to work with, although running them for 3-5 minutes in an ultrasound makes the seat a little more useable, as they appear to be coated with something.

 

[elan]

All D400s are not created equal. The early D400s with the one piece all metal aspirator/metal orifice and the single flat lever are very nice, very easy to tune and can produce a lower inhalation effort than the later two piece/plastic orifice aspirator and two flat levered D400s.

I suspect the change in the lever was related to CE freeflow requirements, although it was marketed as increasing the working range of the valve. The CE freeflow requirements were not kind to the D400 - or any other good breathing regulator, and I always got the impression that particularly silly requirement was intended to level the playuing field for lesser performing European models.

The later D400 poppets are also difficult to work with, although running them for 3-5 minutes in an ultrasound makes the seat a little more useable, as they appear to be coated with something.

I have noticed that the D400 guide recommends setting the inhalation effort to 1.0-1.5. This does not make sense to me... it's like putting a 400hp engine into a car and limit it at 200hp. Is it influenced by that infamous CE requirement ?

 

[ams511]

I bought a used Air 1 on eBay a while ago because I was curious and it was cheap. When I put it on a tank to test it I could not believe how easy it was to breath off of. Noticeably better than anything else I own. Granted breathing on the surface is not a great test but still I was shocked at how well a 30 year old design can breath. I will need to pick up another one.

 

[elan]

I bought a used Air 1 on eBay a while ago because I was curious and it was cheap. When I put it on a tank to test it I could not believe how easy it was to breath off of. Noticeably better than anything else I own. Granted breathing on the surface is not a great test but still I was shocked at how well a 30 year old design can breath. I will need to pick up another one.

If you go for another one - pick a pilot with the Air one guts. It is easier to work with the diaphragm on the pilot as the exhaust holes give better access to the retaining clip. I had the same feeling as you had.

I still have another Air one laying around - I think I will put it on my single tank rig.

 

[DA Aquamaster]

I have noticed that the D400 guide recommends setting the inhalation effort to 1.0-1.5. This does not make sense to me... it's like putting a 400hp engine into a car and limit it at 200hp. Is it influenced by that infamous CE requirement ?

As far as I can tell, that was the intent. Most will provide very stable performance with cracking efforts in the .5" to.6" of water range. and setting them at 1.0 to 1.5" of water is almost criminal.

A possible downside is that when set that low they can develop a slight freeflow in mid season, requiring a slight tweak to increase the spring pressure. For that reason some techs would edge the cracking effort to around .7 or .8 to prevent the need for a customer to come in for a mid season adjustment.

 

[elan]

As far as I can tell, that was the intent. Most will provide very stable performance with cracking efforts in the .5" to.6" of water range. and setting them at 1.0 to 1.5" of water is almost criminal.

A possible downside is that when set that low they can develop a slight freeflow in mid season, requiring a slight tweak to increase the spring pressure. For that reason some techs would edge the cracking effort to around .7 or .8 to prevent the need for a customer to come in for a mid season adjustment.

Thanks, it starts making more sense. The D400 I have was serviced by some unknown tech, I will measure the cranking effort, may be it's just set high and this makes it breathing harder than the air 1 I have.

 

[DA Aquamaster]

One thing to remember when adjusting the D400's spring tension is to always end the adjustment with a counter clockwise direction to keep from "winding" the spring. So overshoot the adjustment by 1/4 turn and then back up 1/4 turn counter clockwise.

Also, when adjusting the spring, first make sure you have adequate slack in the lever (more than you think you need). If you don't have enough slack in the lever, the reg will freeflow as tightening the spring will reduce the play in the lever and you'll end up with a cracking effort that is a lot higher than it needs to be. The lever adjustment should be loose to start with and should then be the last adjustment made reducing the play to about 1/8" after you have adjusted the spring pressure to the minimum needed to close the valve.