How to tell its time to replace DOS heads

**Tha Bizness** · 04-06-2017

Sorry for the long book....

Last month I had a tank destroying 700ml OD of vodka from one of my DOS heads. My water looked like skim milk. I was able to save the tank by doing automated water changes, running a vortex diatom filter 24/7 (minus changing the powder) and a AquaUV 57w, Skimming wet, and daily multiple filter stock changes. My only losses was a Sailfin Tang and a single small frag of pink lemonade. In the beginning I would have thought I had a total loss. After the OD I shut the head down and didn't worry about it. To confirm it was a bad head after the week from hell saving the tank I used RODI water to test dosing 20ml of RODI into a container outside of the tank. During this test it dosed the 750ml of RODI bottle.

Before I started dosing vodka I did automatic water changes with the DOS on my 180g reef. I came up with a way to do AWC with the PMUP so I started dosing with the DOS again and that's when the disaster happened. This unit is in the batch of the first DOS units and I did get the heads replaced after the initial production issues in 2015. I still have the invoice.

I got a replacement head yesterday from BRS and swapped them out and to my amazement 2 small pieces were broken off on the DOS head and required tweezers to get out. It also had spider cracks in the plastic on both sides. The sides had not yet cracked completely off but was most definitely weakened and probably would have been a full break soon. I'm thinking this was due to stress.

The DOS manual says the life of a head is 5000 hours. My AWC took 2 hrs per head. Lets assume I did this everyday (which I didn't but for ease of maths) since 2015 when I replaced the head. Going until today would only be 1652 hours on each head. Lets just say for general principle I ran the head for a +1000 hours since 2015 on "other projects" what ever they may be (I don't think so but lets just add some random time.) That brings the head to 2652 hours or a little over half the life. If I follow the 5000 hour rule I shouldn't have to replace them for years.

I am worried now that the heads may not be as long lived advertised or I should be replacing them sooner. Maybe yearly even tho its no where near 5000 hours. I am concerned now with the stresses that may be put on these heads. What is the communities experiences with these DOS heads now since we are years from initial production? I have read some stories similar to mine but wondering what the over all experience is. How often do others replace the heads and do u wait for the 5000 hr mark? Is there a way to tell pending failure before failure? I doubt if I ever dose Vodka again with DOS but my trust factor in this piece of equipment is waning.

**RussM** · 04-06-2017

Please allow me to correct some incorrect info here. The DŌS manual does not state that the life of a pump head is 5000 hours. The DŌS product web page does give a figure of 5000 hours, but that is the MTBF (estimated mean time between failures) of the stepper motors, not the pump heads; MTBF is not the same as service life or a recommended replacement interval.

The useful life of a DŌS pump head is highly dependent on how it is used. A pump head which is used for dosing of small amounts of liquids at low speed (such as 25ml/day of an additive at very low speed) is most likely going to last longer than one used in a manner which is going to have more wear and tear, i.e. for extended operations at high speed (such as larger automatic water changes).

**Tha Bizness** · 04-06-2017

Understand.

So is there a low/medium/high usage of useful life in the pump head from the manufacture? Just looking for a guide not hard numbers. I'm no longer doing water changes with this so for an example lets say a 20ml of dosing/day

**Delmo** · 04-06-2017

I'm lost. If some part of the pump head was damaged (mechanical failure), then it should dose less than expected. I don't get how it overdosed. Seems like a programming error or glitch...? (And it was obviously mechanically sound enough to dose too much)
What am I misunderstanding?
I too have a serial number less than 5000 and swapped the recalled heads. I have new replacement heads at the ready as well.

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**Tha Bizness** · 04-06-2017

It dosed everything in the container similar to a siphon. It didn't stop till empty and did it twice with that bad head. Once with vodka and once with rodi water into another container to as test. With new head its working correctly. I currently have it working dosing RODI as a test into a outside container.

**Simon P** · 04-06-2017

[QUOTE=Delmo;117940]I'm lost. If some part of the pump head was damaged (mechanical failure), then it should dose less than expected. I don't get how it overdosed. Seems like a programming error or glitch...? (And it was obviously mechanically sound enough to dose too much)
What am I misunderstanding?
I too have a serial number less than 5000 and swapped the recalled heads. I have new replacement heads at the ready as well.

Sent from my SM

I agree. I have 2 sub 5000 serial units and everytime I've had a head failure it has underdosed, not overdosed. Could the over dosing have been caused by siphoning through the head from the dosing container?
FWIW I have a few fairly busy DOS units doing upwards of 8 gallons a day at high speeds and I find that 4-6 months is the max I can get from a head.

**Tha Bizness** · 04-06-2017

I think it was caused by siphoning.

**wwanthony** · 04-06-2017

Originally Posted by RussM

Please allow me to correct some incorrect info here. The DŌS manual does not state that the life of a pump head is 5000 hours. The DŌS product web page does give a figure of 5000 hours, but that is the MTBF (estimated mean time between failures) of the stepper motors, not the pump heads; MTBF is not the same as service life or a recommended replacement interval.

The useful life of a DŌS pump head is highly dependent on how it is used. A pump head which is used for dosing of small amounts of liquids at low speed (such as 25ml/day of an additive at very low speed) is most likely going to last longer than one used in a manner which is going to have more wear and tear, i.e. for extended operations at high speed (such as larger automatic water changes).

If I understand you correctly, you are saying that if you use the pump head less (slower and/or less often ???), it will last longer. I am not sure what to think about that. My first thought is, no kidding. Another way to look it: You can get more out of a tank of gas if you don't speed. I can get behind that. And if so, then folks would certainly want to know where the sweet spot is.

**Delmo** · 04-06-2017

Oh, then lower your container to the DT water level to prevent that from happening ever again. I have my nsw barrel about half way up the tank height when full in the garage, just in case. I also have a valve on the nsw outlet of the pump, just in case.

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**Delmo** · 04-06-2017

I just took my dosing heads off and checked them out. They Look in really great shape, Brand new Looking in fact, with the factory grease, and no wear. I run mine about 6500mL in 75 min, so pretty fast, once a day, most days for AWC.

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**badstraw** · 04-08-2017

[QUOTE=Simon P;117942]

Originally Posted by Delmo

I'm lost. If some part of the pump head was damaged (mechanical failure), then it should dose less than expected. I don't get how it overdosed. Seems like a programming error or glitch...? (And it was obviously mechanically sound enough to dose too much)
What am I misunderstanding?
I too have a serial number less than 5000 and swapped the recalled heads. I have new replacement heads at the ready as well.

Sent from my SM

I agree. I have 2 sub 5000 serial units and everytime I've had a head failure it has underdosed, not overdosed. Could the over dosing have been caused by siphoning through the head from the dosing container?
FWIW I have a few fairly busy DOS units doing upwards of 8 gallons a day at high speeds and I find that 4-6 months is the max I can get from a head.

I was planning to order a DOS for 1 gallon daily AWC, but now I'm not sure to get one..

**Simon P** · 04-08-2017

Originally Posted by badstraw

I was planning to order a DOS for 1 gallon daily AWC, but now I'm not sure to get one..

For 30$ every 4-6 months I don't consider replacing a DOS head to be deal breaker. So long as I get a few years from my DOS pumps I feel this will have been a really good investment for me. It certainly has made running a calcium reactor a breeze, not to mention the sulfur and alcohol denitrators I use them on.

**Delmo** · 04-09-2017

Badstraw
I've been using mine for over a year to do 1.5 gallon awc every day and see no wear on the pump heads.

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**KrazyKuch** · 04-10-2017

Originally Posted by Tha Bizness

I think it was caused by siphoning.

Just throwing this out their but last time a checked you can't siphon through a dosing unit. The hose should be pinched at all times inside the unit

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**Tha Bizness** · 04-10-2017

The head had broken pieces in it when I removed it during replacement so anything goes i guess. The dosing container was on the same level as the DOS and from what i have read in certain failures when the container is level with the DOS this can happen.

I have replaced the head and lowered the containers and i have not had a problem since in testing and now regular dosing. Im pretty positive the head was the issue.

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