Air sensor info Remstar Auto (classic)

I’ve identified the flow and pressure sensors on the PCB of two bread-loaf Remstar Auto machines I looked at.
The gray sensor with side-oriented tubes is Honeywell AWM92100V mass airflow sensor. Intended for medical application with dry gas only - will be damaged by water, may be affected by dust, says Honeywell (who want a five micron filter upstream). Air goes through the AWM9100V across a very small chip. It is available for around $70.

(Beware that some people call the machine’s output tube a flow sensor, but it is only a restrictor that generates a pressure difference between the two small tubes to cause some flow through the actual sensor.)

The round black sensor with vertical tube is marked SPV6004G, with the logo of Freescale Semiconductor who made it for Respironics, no details available. Its plumbing is dead-ended so probably at much less risk than the flow sensor even if it is sensitive to water.

Replacing these sensors would need soldering equipment and skills to remove the multiple-lead part and get solder out of PCB holes, then solder replacement in getting a good connection without overheating the part. Given that effort and the cost of the flow sensor it is a marginal notion for an old machine even if working cheap for oneself.

For protection from water, I notice availability of a humidifier reservoir with some kind of check valve, 1035162 replaces 1005792 according to http://www.cpap-supply.com who don’t explain it well. Also there is a foam seal for the data card slot, seen on one unit not on an earlier one (not shown in 7/12/04 version of service manual).

Not a bad machine, but has examples of the need for thoroughness in product development. It only takes one detail of thousands in the design to have poor reliability.

So now we know why there's a fine filter. It ain't to protect us -- it's to protect the MAF sensor. Doesn't that just warm the cockles of your heart!

Anyway, thanks for the info. I was wondering about the technology of the flow sensor. I guess I wasn't curious enough to disassemble my machine.

Clarifying, the “check valve” I saw advertised was described as a “flapper” and seems to be in the chamber not between chamber and machine (the illustration of the unit includes two standard adapters to couple chamber to machine supplied with it). Claimed to be removable for cleaning.

They also sell a “CPAP pressure valve” which is an inline hose coupling described as having “a spring-loaded valve that helps prevent the backflow of oxygen or water into the ...machine...when turned off”, vented somehow when pressure less than 2 cm, but not an anti-asphyxiation vent. Too large to fit between Remstar classic humidifier and machine, so only useful for a humidifier that sits separate from the machine.

You don’t want to look for the flow sensor’s identification on a working machine, it is on the bottom side of the sensor.

FYI the restrictor that generates the pressure differential is called a “flow elment” by Respironics. Regarding filters, the outer foam one may be referred to as a “pollen” filter, the inner white one “ultrafine”.

Actually there is a flapper inside my humidifier.
However, I can pour the water out of the humidifier by the inlet port.
I have not disassembled to investigate.

BigNortherner wrote:For protection from water, I notice availability of a humidifier reservoir with some kind of check valve, 1035162 replaces 1005792 according to http://www.cpap-supply.com who don’t explain it well.

That sounds like it is for an M series machine. When you mentioned "breadloaf" I thought you were talking about the older "tank" style machines.

I have a legacy REMstar with both flavors of humidifier tank.

The flapper is a removable assembly. The flapper is a two position valve.

With blower pressure the flapper goes up and airflow goes into the tank. The flapper seals and blocks an air vent coming out of the tank to the room air.

With no pressure, the flapper goes down and seals the opening from the blower unit into the tank. The air vent between the chamber and room air opens up. If you blow air into the mask end of your hose, the air will go through the tank, out the vent, but not through the blower unit. If you turn the machine over while turned off, the water will flow out the air vent into the room, but not through the air connection into the blower unit.

That's in theory. In practice, I'm not that confident the flapper will always seal water out of the machine. Also, water pours out the air vent and would tend to pour all over the outside of the machine. I'm sure that beats pouring it directly into the blower unit, though.

There are two flavors of humidifier tank and two flavors of "water" blocker thingy. The chambers come with the water blocker, but I believe you can buy spares for the new flapper style. The parts are not interchangeable, except probably the baseplate. The old style had a silicone insert that went between the blower and the chamber. That insert needs to be removed before using the new style chamber.

The old flavor water thingy was just a snap in baffle that looks to me like it would mostly help keep sloshes out of the blower unit, not "turn the machine over" types of spills. No moving parts, no valve. I'd recommend anyone using the old style buy the new tank and valve.

archangle wrote:I have a legacy REMstar with both flavors of humidifier I'd recommend anyone using the old style buy the new tank and valve.

I would disagree with you on this. The new style tank with the flapper disables the Auto On" feature and also leaks air out the "Big" hole in the top. I would trade anyone the new one for the old model. I have never had a problem spilling water back into my machine because I tie my hose down so I can't pull the machine off the table.

I have one with a bad air flow sensor and I thought I might try to replace it. Got the maker and model but when I investigated what it would take to calibrate it I came to the conclusion it might not be practical. Lots of equipment that I had a problem locating as well as cost.

Jerry

6PtStar wrote:

archangle wrote:I have a legacy REMstar with both flavors of humidifier I'd recommend anyone using the old style buy the new tank and valve.

I would disagree with you on this. The new style tank with the flapper disables the Auto On" feature and also leaks air out the "Big" hole in the top. I would trade anyone the new one for the old model. I have never had a problem spilling water back into my machine because I tie my hose down so I can't pull the machine off the table.

Mine doesn't leak any air out the hole on top. Try playing with the flapper a little.

Does the legacy REMstar Auto do "Auto On?" It doesn't seem to be in the clinician's menu or the manual. Is there a later version? How do you turn it on?

archangle wrote:Does the legacy REMstar Auto do "Auto On?" It doesn't seem to be in the clinician's menu or the manual. Is there a later version? How do you turn it on?

It is a safety feature so there is no on/off. Default is ON.

Yes, the Legacy does do "Auto On". It can not be turned on or off. It is on all the time except when the flapper won't let you breathe back through the machine to the sensor. If you take the chamber off and hook the hose directly to the machine and take atbout 3 breaths it will turn on. Used to be considered a safety thing because it a power surge cut the machine off it would turn back on almost without wakeing up.

When I read my card with Encore Pro sometimes it would look OK. Other times the standard leak line would be much higher which came from the flapper leak. I changed the flapper and it still did not help. Finally found an old model chamber.......no more leaks.

Jerry

Interesting. The legacy REMstar Plus doesn't have auto on at all, but you're right, the Auto does.

The Pro2 has "Auto On" also. Don't knbow about the "Plus"......never owned one or had the desire to own one.

Jerry