Prism Scrubber etc

reefrat

Hi all

I'm doing the Rebreather research thing before I buy and am oscillating between the KC and a few others. At the moment I may possibly have the chance of buying an almost new Topaz..not sure yet...
This puts the Prism unit back in contention, I previously ruled it out because 9+ months of waiting for delivery is just too long for me!

Anyway, the scrubber. What's with the locking mechanism where it attaches to the head (the whole thing looks like deluxe tupperware), is it REALLY secure and tough?

And the secondary analogue handset, when your checking that is it a PITA to select all the sensors separately?

Lastly, the proprietary sensors- is this an issue as opposed to most other units on the the market that use the more commonly available Teledyne units and can others be used in the unlikely event that something ever happens to SMI?

Don't get me wrong, I've read a lot about the Prism- seen it dived once and so far it's a very attractive option, these are the only (maybe) potential issues with it that I can see!

silent running

Hello Mr. reefrat, nice handle.

?1-Scrubber pins/ bucket fastening: Yes they are secure, the suction of 2 O-rings and a bunch of silicone grease is serious enough that it needs a big strip of grippy textured tape on the bucket and some solid taps on the bottom to turn the damn thing. I have cursed at it many times. And, IMHO, the twisting motion required to get the bucket off/on is less likely to pinch/stress the O-rings. Is the whole asembly strong enough to be dropped a bunch of times on concrete? No, but the bucket is very thick and was repeatedly dropped from 20ft on concrete during USN testing o see if it broke/deformed. It did not. Is the Meg scrubber/head bucket assembly tougher? Yes. But it weighs a lot more and can't be easily repaired in the field if you dent it. Virtually any injury to the head and bucket of the Prism can be repaired with epoxy in a few minutes.

?2-2dry is easy to scroll through, the selector wheel is big and notched, I can move through all 3 in 2 seconds. And you get to see how fast each one comes up as the circuit is completed, giving you more info about the health of each sensor. IMHO, this is just as efficeint a cognative process as looking as 3 sets of 3 place digits-9 numbers-without the benefit of seeing each sensor come up to a value each time you scroll through.

?3-Prism sensors are indeed proprietary. But they are similar enough to those used in the MKs that you can use MK sensors in the Prism, so I'm told. SMI have an exclusive agreement with a manufacturer for their sensors, which are a little bit different, to make them only for SMI. But I doubt they would stop making the sensors if SMI went belly up any more than those who make sensors for the MKs, even though thay are out of production and were never retailed to the consumer market. IOW, I wouldn't worry about it.

Good questions reefrat, happy trails, -Andy

Chris

It works pretty well, I had one leak but thats cause I let the Orings Dryout, you got to keep the lube up on them or they shrink, well thats what happend to mine anyway. Eventually the pins that hold the bucket break but you just drill em out and replace them with Stainless Steel Screws, these work much better.
Yea look at replacing it with one from SubSea as soon as you can, digital readout all three cells in front of you.. When Jason finally gets stock of the PRISM ones.
The SMS202 Sensors are IMNSHO the best part of the PRISM, the things are huge and if you get good ones will last for years, unlike R22D's that shit themselves whenever they feel like it.
I sold mine after 18 months and went to the Meg. The PRISM underwater is a great unit but the thing is just so fragile in its construction compared to other units out there. If you end up buying the PRISM make sure you get the cowling and NEVER dive without it, also carry a tube of DP190 and a spare secondary.

Cheers
Chriso

__________________
Megalodon
Sorb and Sensors whilst in Australia www.divetub.com.au
Diving & Photography @ www.uwphotog.com

reefrat

Silent-Running
Thanks for that!

Have you used the HUD on the Prism for manual setpoint control? Does it provide enough information for this or do people usually use the secondary analogue display for manual control?

reefrat

Chris said

"I sold mine after 18 months and went to the Meg. The PRISM underwater is a great unit but the thing is just so fragile in its construction compared to other units out there. If you end up buying the PRISM make sure you get the cowling and NEVER dive without it, also carry a tube of DP190 and a spare secondary."

Strange how some people talk about the construction being strong and others say it is fragile?? Would you say that the fragility issue would be "solved" provided the cowling was used!!

I thought about the Meg Copis but I want a unit that I can use the HUD as a primary p02 display and the meg HUD looks a little confusing to me. The best I've seen so far (IM[unqualified]O) is the Shearwater- just makes sense to me.

Chris

Ahh you can't

You can turn the unit off and fly it manually with the Secondary but then the HUD is also off. As long as the PRISM is turned on it will run the setpoint selected during Predive, you cant change it during the dive.

If the setpoint for the dive is say 1.2 on your predive and run try it manually at 1.3 with the unit turned on then the HUD will display the blue Red instead of green.

Cheers
Chriso

__________________
Megalodon
Sorb and Sensors whilst in Australia www.divetub.com.au
Diving & Photography @ www.uwphotog.com

Chris

They dropped the bucket a couple of times on the concrete and it was fine, but they never dropped the head, it would be a big cleanup with a dustpan and brush if you did.

The cowling will help if you are dragging the PRISM through an overhead environment and banging it on wrecks, but as for falling out of a tank rack or the back of the car well.... I have seen a good number of PRISM's (including my own once I sold it) with cracked heads, easy enough fixed with an Epoxy, you can just glue it right back together and not miss any diving. I just prefer to own a unit I have seen falling multiple times from tank racks landing on a metal deck on its head. Then strapped on for a 120m dive. I doubt I could have done that with the PRISM.

The Shearwater is nice I agree, it took me about 5 dives to get used to the Meg HUD, I now prefer it to the PRISM. The Meg tells me the Po2 reading of each idividual cell, so the HUD can certainly be used as the Primary on the Copis with backup glances to the handset to confrim.

Cheers
Chriso

__________________
Megalodon
Sorb and Sensors whilst in Australia www.divetub.com.au
Diving & Photography @ www.uwphotog.com

silent running

You're welcome reefrat. Yes, the HUD would provide you with more than enough info for manual operation, but as Chris said, you can't disable the solenoid, so you would have to plan to fly it above the pre-dive determined SP and put up with the red warning light on the HUD signaling high PO2. Maybe not so bad, as it's also a safety margin of sorts, and some CCR divers choose to dive this way.

The Prism has very basic electronics-set point only control and it does this very well, perhaps better than any other unit. In exchange for this simplicity, you're 2dry is driven directly off the sensor mv's for an accurate PO2 and you don't have any multi function handsets. So, you can't do anything during the dive except turn it on or off and fly it manually. But during the dive, the HUD will tell you if you're on, below or above SP and by how much and whether a sensor has been voted out and whether the battery is low, all at once if necessary.

If you want a manually controlled CCR with a HUD as a stock, I'm not sure what the options are. I don't think any MCCRs come stock with a HUD. Maybe the rEvo does? In general, HUDs seem to run contrary to MCCR design philosphy-displays for each sensor that require the user to look at them frequently=redudnadncy as in the KISS. MCCRs tend to keep battery driven things to minimum and spend their time perfecting the O2 constant mass flow injection process....

PhilSiswick

Correct, the rEvo does, on the rEvodream.

Cheers,

__________________
Phil

No comment on open circuit... it's an evolutionary dead end not really worth discussing here. Dave Sutton, 2007

I have always felt that the dive I am on is not nearly important as the dives I plan to be on the rest of my life. Tom Rose, 2007

www.hugsac.org.uk

Dave Sutton

Teledyne sensors will work just fine. Nothing special about the SM stuff other than the fact that SM would like you to buy them.

The analog secondary WILL fail after you drop it. They work *just fine* and are well proven (being a copy of the Mark-15/CCR-1000 scheme) but they *will* break when dropped at their own cable length to the deck. Trust me on this. There are digital alternatives available from SARTEK and COLKAN. Either would be preferable. Change the battery once a year and forget about them. Analog needles are obsolete.

With all due respect to a prior respondant, there is *no* value in watching the needle "jump rate" as the sensor is selected, again with all due respect that shows a lack of understanding of how a jeweled meter movement functions. All you are seeing is the mechanical aspect of the meter movement *itself*, IE the strength of the spring that returns the needle to zero when voltage is removed. The rate of the needle moving back to the measured position is again simply a mechanical spring function of the meter movement and has no bearing on cell viability. None, zero, zippo, nada, got it? If anyone was told otherwise by the OEM, it's a matter of simple salesmanship. Just ain't so. Not the first time that people promote what they happen to have on hand as a "design feature".....


Opinion? The Prism is little more than a "serial manufactured homebuilt" with construction material selection and methods that are, err..... well let's say that I would be able to make a more robust rig in my garage. Electronics are simple and reliable, but there are other choices out there......



Dave Sutton