scooba 5900 has solution left in tank

[rostropovich66]

I've had my scooba 5900 for a year now. All is ok except scooba now finishes its cleaning cycle in the usual way (blue light, little tune!) but has about 2 inches of solution left in the tank when held upright. Is there a fix for this?
I'm feeling quite confident of mending things having just opened up my roomba, and following the excellent instructions on this site, repaired a broken string/brush raising issue!

Emtying the dirty tank & restarting doesn't work. Is does start again but soon goes into flashing blue light mode & puts down very little solution, still leaving lots in the clean tank.

Thanks.

[Gordon]

... scooba 5900 ... . All is ok except scooba now finishes ... but has about 2 inches of solution left in the tank when held upright. Is there a fix for this?

Probably not, other than to try a new Tank. But, since we don't know the source of your 5900's particular problem, it is too early to claim that a Tank replacement will fix the problem.

As I currently see it, this Scooba is suffering from a reduction in gravity-induced flow rate as the pressure-head (proportional to column height of liquid in clean chamber) diminishes with consumption of cleaning solution. Three elements may impact that delivery rate, and, since they work effectively in parallel, their impacts may combine to develop the overall rate reduction! The physical hardware under suspicion are:
a) The Clean Chamber's Air Vent Valve;
b) the Clean Chamber's Solution Outlet Valve (it's degree of opening, and screen-filter"impedance"), and
c) the ability of the robot's Solution Inlet Lance to push open item (b) the nominally required amount.

Refer to this post...
http://www.robotreviews.com/chat/viewto ... 846#p28846
to read about the Inlet Lance (and mentally correct the stated limitation about not being able to repair a broken Lance (Solution Inlet Fitting) -- it can now be done, with a great amount of work, plus some money). If you need a graphic showing a Lance 's broken tip, I can probably post a photo.

You'll find some words telling how to verify "degree of opening" (in (b) above) at this URL:
http://mysite.verizon.net/gsplews/0.6cleangTAs_port.htm

Then, the combination of (changed with time) filter-screen impedance, in combination with (b), Outlet Valve opening, with or w/o the Vent, (a), in play, can be examined by using guidance found in this thread:
http://www.robotreviews.com/chat/viewtopic.php?t=10228

Your flow rate testing should probably be done using roughly the residual volume of solution that you now see the 5900 leaving in its Clean Chamber. Don't expect much flow, after all, it takes Scooba roughly an hour to dispense about 900 mL (giving only ~0.25 mL/s).

BTW, thank you for a well crafted fault assessment.

Hopefully, you will be able to verify that the robot section is OK, and that its fault is within the Tank.

[rostropovich66]

Many thanks for your prompt & superbly intelligent response!

Upon closer inspection, the little round vent-valve on the underside of the tank leaks cleaning solution when the tank is inverted.

This may lead to a reduction in pressure & hence my problem?

This also looks unfixable & a new tank required.

Not that expensive I know, but the postage to the UK is a little painful!!

ouch!!!

[mfortuna]

My 350 tank seems to weep a little bit there but otherwise works fine. I'm not sure why the robot would stop if there was still fluid in the tank. I believe it uses a sensor to determine when the tank is empty.

[Gordon]

... I'm not sure why the robot would stop if there was still fluid in the tank. I believe it uses a sensor to determine when the tank is empty.

Mike, maybe the following information about that sensor's location will help you understand why Scooba will end its mission with unused fluid remaining in the chamber.

The clean-solution sensor is not in the tank, it is at the base of the Solution Inlet Fitting in the robot. If that sensor-head's electrodes are not kept wet (maintaining a conductive path between them), Scooba will assume the clean-chamber has emptied.

[Gordon]

...the little round vent-valve on the underside of the tank leaks cleaning solution when the tank is inverted. ... & hence my problem? ...

You may demonstrate its impact by side-stepping its service if you run Scooba with its Clean Chamber's stopper left open -- as one of the other posters reported. That takes the venting portion of that valve totally out of play.

The vent valve is a one-way "check-valve" having as main purpose to allow air to enter the chamber as fluid is withdrawn. Its sealing capability (reverse-flow check) is not particularly important -- being more of a mess avoidance courtesy, than a functional requirement.

[mfortuna]

Thanks Gordon, I did not know that detail. I remember seeing some electrical contacts on the tank and assumed their function was to detect an empty tank. Maybe they are actually for the full tank indication.

[TechGuy]

My Scooba 5900 is leaving cleaning solution in the clean tank and starts the drying cycle early. I have to stop it and open the clean cap to release the vacuum created by the cleaning solution exiting the clean tank. Then, restarts it to complete the remaining cleaning mission.

The vent valve did not open. I did use can air to blow air through the 3 small holes on the vent valve. They are not clogged. I read this thread and the referenced threads a few times and still don't know how to correct the problem.

[mfortuna]

Someone mentioned drilling a small hole in the clean tank cap will fix the issue.

[TechGuy]

Someone mentioned drilling a small hole in the clean tank cap will fix the issue.

I read that thread too. But I like to figure out where is the source of this problem.

I used a can air to clear the holes of the air vent valve. This does not correct the problem. I checked the clean tank outlet valve and the pump inlet lance. I do not find anything which is abnormal.

The water pump may have small blockage to reduce the suction pressure enough to prevent the air vent valve from open. The reduced suction pressure may be due to loose fitting between the clean tank outlet and the water pump inlet. The fitting between he clean tank outlet valve and the lance is a source of air leak. I do not know whether there is any fitting may become loose over time as I have not open my Scooba to inspect inside.

I used a syringe to force some air into the clean tank outlet valve. I heard a popping sound when air was forced in. I can feel water on the lance body between tank closure. I am charging the battery now and report the result after the next mission.

[Gordon]

... But I like to figure out where is the source of this problem. ...I used a can air to clear the holes of the air vent valve. This does not correct the problem.

You may have forced more air through that value than has passed during its entire existence! No problem, just a comment.

I checked the clean tank outlet valve and the pump inlet lance. I do not find anything which is abnormal.

Good and good! But, when examining the lance, did you use optical magnification (to help see any cracking / bending of the tip structure)? If the tip of the lance has gotten deformed, thus lowering its height by even a millimeter, the poppet-valve in the clean tank will not be opened as far as necessary, and thus throttle outflow from the tank. When the tank is full, the height of the solution develops a greater pressure-head down at the outlet, and that extra pressure will tend to overcome the mentioned 'throttling'. But, has height decreases -- with extended cleaning time -- the pressure head diminishes, flow diminishes, and the fluid in the drain-line may be consumed -- thus draining solution out of the sensor chamber (below the lance, and in its elbow-body) and Scooba's controller is notified: "no solution".

So, double check that lance.

The water pump may have small blockage to reduce the suction pressure ...

Scooba's pump does not create "suction", it depends on gravity-feed.
EDIT: By saying "does not create "suction"", I implied ZERO suction -- which is NOT the case. Enough suction is created to empty the solution feed-line and inlet elbow after solution exhaustion; however, that suction magnitude is insufficient to provide "lift" against gravity, if attempting to pump liquid from a vessel located below the pump-diaphragm(s).

... I do not know whether there is any fitting may become loose over time as I have not open my Scooba to inspect inside. ...I used a syringe to force some air into the clean tank outlet valve. I heard a popping sound when air was forced in. ... .

I think there has been one report about someone forcing off one of the flexible tubes (Tygon plastic) which simply slip onto tubulatures that are part of the aft pump-casting. You can see them here in Figure 2.

But, if it is the feed-tube TO the pump that gets loose, contents of the clean tank will drain rapidly onto the floor (before solution gets to the floor, it does a lot of wetting inside Scoobas machinery 'compartment' -- Scooba is built to handle that!).

[TechGuy]

So, double check that lance.

I inspect the lance again under my workbench lamp with built-in magnifier. It does not have any hairline cracks or deformed. I do not have another Scooba to compare. I am not sure whether it is deformed. But it looks symmetrical to me. I may glue a small cap on the tip to try it out.

[Gordon]

Here's a look at a virginal lance:

...and here's one of a badly cracked lance tip.


Try to imagine a lance-tip somewhere between the two conditions.

You may need more magnification than can be obtained with the device you used. I'm thinking more in the 5X to 10X power region. If your digital camera has a macro function you might try photographing the lance, and then look at the jpeg image.

[Gordon]

TechGuy, at first you said this:

...
The vent valve did not open. I did use can air to blow air through the 3 small holes on the vent valve. They are not clogged. I read this thread and the referenced threads a few times and still don't know how to correct the problem.

Ever since I first saw a Scooba Tank and its vent-valve, I have wanted to see more of it! So, to satisfy that curiosity, and to show you it is such a simple piece of hardware that its very unlikely to become a problem, I did a vent-valve-ectomy; and, then took some photos that have not been seen this side of the iRobot Scooba-labs!

This is then this forum's premier, valve-disc coming out showing -- just for you!

The first image reveals what the interior (normally 'top') surface of the valve-disc looks like while still assembled to the tank wall:

This next image is of the disc's sealing surface:

And, here is a profile shot of the valve-disc:

The disc's rim is very compliant (not stiff).

Don't you agree that if the three air-inlet holes are not clogged, and, there is no particle stuck under the rim of the valve-disc, this valve simply must do all it was ever intended to do?

[Gordon]

TechGuy, here's another photo of Scooba's 'lance' (from which to learn):

This is a partial view of what's under the 'hood', and not only has the 'hood' been removed, but so has the protective-cover over Scooba's main-electronics.

Find the solution-inlet lance at lower right. Notice how its tip has been "dimpled". No cracking is evident, but the working height of the tip has been reduced. The condition of this lance is in between the previously shown NEW and CRACKED stages.

I think this particular Scooba got decommissioned by that small amount of damage.

[TechGuy]

Gordon,
Thank you for the photos.
It did not ended the last couple of missions early since I pushed air through the clean tank outlet valve with a syringe.
Here is a photo of the lance on my Scooba. It is hard to determine whether the lance had been flattened by a mm or not.

[Gordon]

Gordon, ...Thank you for the photos.

You are quite welcome.

It did not end... the last couple of missions early since I pushed air through the clean tank outlet valve with a syringe.

While it is good that the air-purge worked, I have no supporting explanation!

Here is a photo of the lance on my Scooba. It is hard to determine whether the lance had been flattened by a mm or not. ...

It looks like it is in new condition, to me!

[cynbeall]

I have the exact problem. I am a Interior Designer. What do I do for help? I will NOT be taking my Scooba apart.

[cynbeall]

I have the exact problem. I am a Interior Designer. What do I do for help? I will NOT be taking my Scooba apart.

[Gordon]

I have the exact problem. ... What do I do for help? ...

Cynthia, are you certain that your Scooba has "the exact problem"?

If so, you ought to be able to follow what TechGuy did, since his problem seemed to go away following his DIY treatment. We don't know what the OP's (rostropovich66) Scooba was doing, since he bailed w/o a determination.

If your Scooba has no active warranty, I expect you are stuck with us for help. If that is the case, have you read all the above posts, and taken any side-trip links? I think this thread has covered most of the hardware damage that can prevent a load of cleaning solution from being consumed.

About the only other influences that come to mind -- and which did not get discussed in this thread -- are a) Scooba working in a small area (so it decides it has cleaned enough and quits early), and b) a unique residue in the dirty-tank which triggers a false (but effective) "tank-full", after a partial filling wets that remaining debris, which then causes Scooba to quit sooner than expected.

So, give us some words about your Scooba (model, history, normal treatment), words about what you understand, or don't understand in the above posted information, and indicate whether you have taken a real close look at your Scooba's solution inlet lance.

Oh yeah! Welcome to rr!