#0034: Repair and analysis of a tap cartridge
Preamble
I recently had to repair a constantly dripping kitchen faucet, and thought that I may as well document it. Especially since I found the construction of the cartridges within the tap to be rather interesting. Although I must say that the title does make me feel a bit silly.
Tools and Materials used
Tools:
- crescent wrench / 17mm wrench
- nylon spudger / pry tool
- phillips screwdriver
- soft bristle toothbrush
- plastic container
- pipette
- teaspoon
Materials:
- petroleum jelly / plumber’s grease
- vinegar
- water
Tap cartridge inspection
I’d like to start by examining the water faucet’s cartridges themselves, as this information will be relevant later during the repair. The two pictured cartridges were taken from a quarter turn kitchen tap. This is a tap that only requires the handle to be turned 90 degrees around it’s axis, in order for it to go from a fully shut to a fully open state, and vice versa.
This type of cartridge is designed so that water flows into it from the central hole at it’s bottom inlet. This water then flows up inside it’s shaft, and through the two holes within the first ceramic disc. It is then diverted out through the two radial holes on it’s side via the second ceramic disc. At which point the water has a direct route to the faucet head.
This particular type of cartridge has two ceramic/plastic discs within it, that in conjunction with each other operate as a single water control valve. They do this by establishing a water tight seal between them; a press fit seal that is created by the two discs merely pressing against each other in a way that eliminates any gaps between them.
This seal is demonstrated within the video below, where you can see a suction effect take place between the two discs. This suction helps the two discs adhere to each other when wet. This is only possible due to the absolutely smooth surface of the first disc, coupled with the hollow cups present on the second disc’s contacting surface.
These two ceramic valve discs are both keyed to fit into their brass metal shaft in one particular orientation. This orientation has the bottom disc operate as a fixed or stationary valve. Whose job it is to split the ingressing water into two separate streams. It does this via the two distinct triangular quarter-circle holes within it. This lower disc is keyed to fit into the inner wall of the cartridge’s cylindrical housing in a way that makes it immovable.
Whereas the top disc is keyed into the rotating tap handle cylinder attachment. This allows the tap handle to control the rotation of the upper disc. This upper disc is cut in a way that either blocks the two water channels provided by the bottom disc when closed; or when open: diverts water from the holes of the bottom disc outwards to the radial holes in the cartridge housing. This water is then further diverted up and out of the tap for use.
The reason why it only takes a quarter turn to fully open the water channels of this type of cartridge: is due to the placement of holes and channels within these ceramic discs. The first (bottom) disc has two oppositely placed holes within it. Each taking up approximately a quarter section of the circular valve.
This quartering is then reflected within the top ceramic disc. Which consists of two opposing cupped flat plates, and two opposing angled wedges: which veer off to the radial holes within the brass cartridge housing. And since these channels take up opposing quarters of their discs – it only takes a quarter turn to either align both holes of the bottom plate with the upper disc’s water outlet ramps, which then allows water to pass; or with the flat plates, which then blocks the water at both holes.
Cartridge operation demo video
Valve operation demo video
Suction effect demo video
Dripping fault Analysis
Dripping fault cause theory
The fault that causes a dripping tap can be due to a number of different factors. Probably the most straight forward scenario includes water simply making it’s way around the rubber o-rings and/or water gasket. This could happen if the rubbers have gotten old or heat damaged, and started contracting or cracking as a result. Alternatively, they could’ve been disturbed or are otherwise not seated correctly in order to form an effective water barrier.
This means that whatever water does manage to get around these seals can then bypass the cartridge altogether and shortcut it’s way to the faucet head. The severity of the leak in this case would be directly proportionate to the ineffectiveness of the rubbers to seal out water.
Another issue could be within the cartridge itself. With water entering the cartridge and then passing through the cartridge valve by squeezing between the two ceramic disc plates due to an imperfect seal. This pressure fit seal between the two disc plates could be undermined by a number of different factors.
The most likely of which are a build up of limescale on the the ceramic discs themselves. Limescale is a broad term to encompass residual build up of the carbonates present in drinking water; such as calcium and magnesium carbonate. Water rich in minerals like this is often referred to as “hard water”.
Limescale build up on the contact surfaces between the ceramic discs, can cause them to then become uneven as the limescale adheres to them. Specifically the drip issue is caused because the valleys in this now uneven surface provide the water a small pathway across the pressure seal’s threshold when it is closed.
Another issue that could cause the valve to no longer function effectively is scoring of the inter-disc surface. Essentially scratches that then allow some water to pass through their valleys when the valve is closed. A likely cause of this could be something as basic as wear and tear. The two discs grinding each other down over an extended period period of time due to standard use. This happening with just the minor friction created from repeated opening and closing over time, eventually compromising the watertight seal as disc surface material is lost.
Before moving on, I should mention that this section is largely speculation. Basically educated guesses based on my observations during the disassembly. That being said these theories above are the one’s that I went into this repair with.
Dripping fault effect
A continuous drip may initially seem like a minor fault, because it is. However, this fault incurs a waste of resources. A slow but continuous one, that is hard to easily assess. Simply put it wastes water, and probably more than you might expect as well. Just because it only wastes a drop at a time, it doesn’t mean that it isn’t wasting a lot cumulatively. It just makes it difficult to easily see the totality of wastage.
Sampling methodology
Let’s try to get a rough idea of how much water is lost due to this fault. Note that this is not going to be very scientific. It is just a test to get a rough idea of water wastage. With that in mind, there are two discrete pieces of information that are required: 1) is the average water droplet volume; and 2) the number of water drips within a set period of time. In this case the sample time will be 1 minute.
I captured a single drop using a teaspoon. Then sampled it using a random plastic pipette that I had on hand. I repeated this a few times and found the droplets to be rather consistent in volume. Unfortunately, due to the pipette’s lack of precision, I was forced to visually estimate this volume between it’s labelled increments.
Collected observations
- This leaky tap consistently provided around 13 drips within any one minute period.
- With each drop having a volume of approximately 0.3 ml each.
Water drip rate and predictive volume lost
- 1 minute: 13 drips @ 3.9 ml
- 1 hour: 780 drips @ 234 ml
- 1 day: 18720 drips @ 5616 ml (~5.6 litres)
- 1 week: 131040 drips @ 39312 ml (~39 litres)
- 1 month: 524160 drips @ 157248 ml (~157 litres)
Leaking faucet demo videos
Droplet sampling demo video
Leak conclusion
Interesting result. If a household either has a limited water supply (e.g. off-grid), or is on a metered supply where they pay for water by volume; then 157 litres lost in wastage in a single month by a single tap is not insignificant.
I hope this has illustrated how important it is to fix even minor faults such as this as soon as possible. 157 litres of water used could very well cost a metered household more money on the fault’s first month on the household’s monthly water consumption bill, than a complete cartridge replacement for that tap otherwise would have.
Repair process
Getting at the parts
First thing first. Common sense. I switched off the water by closing the main water valve for the house. This was located under the kitchen sink for me. This is an essential step in the same way as one would switch off the electricity before working on an electrical outlet, one needs to turn off the water before working on a water outlet. You’d think that was common sense right? But I have seen too many plumber fail videos online that say otherwise.
After giving the kitchen faucet a once over, and looking online I decided that the tap cartridges are the most likely suspects for the drip, so I set upon getting at them. Since I have never taken a kitchen sink tap apart before, I engaged in what I call an exploratory disassembly. Prodding and poking the device looking for hidden clips and screws.
To cut to the point: I used a nylon spudger to pry open the (metal coloured) plastic screw cover on each tap. I recommend using a plastic pry tool to avoid scratching the finish off of any part of the tap. Next. I unscrewed the phillips metal screws which attached each tap handle to the rotatable cartridge cylinder section below them. After setting aside the tap handles, I then removed the full cartridge assembly from the faucet housing using a wrench. As for disassembling the cartridges themselves, they come apart toolessly in-hand. That’s it. Easy.
Inspection
Like every repair, this one begun with a thorough inspection. A basic visual inspection did not reveal anything obviously wrong with either cartridge to my eyes. However once I disassembled both hot and cold units, I noticed that the internal plastic disc valves on the cold water side felt rough to the touch. Likely indicating a build up of limescale. Most notably this was even apparent on the surfaces between the two valves. And since these two surfaces come together to form the press fit seal that controls water flow: I concluded that this was likely the specific cause to this particular leak.
Limescale build up is nothing unusual for my particular location, as I do live in a heavy water area. However the odd part was that all the limescale build up was on the cold water side cartridge of our kitchen tap. With little to none on the hot water cartridge. This is really unusual in my opinion because I believe that higher temperatures should exacerbate limescale build up. The average water kettle should be a testament to this theory. However in this case the limescale build up was only sufficiently present on the cold water side.
A working theory I have concerns the on demand water heater which directly supplies this tap – a boiler which my household recently (1.5 years) had professionally installed. I believe that it has some-kind of water filter (or softener, or descaler…) that has been fitted to minimize limescale build up within the unit as it heats water. This means that the hot water provided by it to the tap would have less mineral contaminants (i.e. be softer) than the cold side. I would verify this, but it is not a pressing issue and not worth digging the unit out at this moment to confirm.
Cleaning the cartridge
Once I decided that it was limescale that was undermining the valves press-fit seal, I decided to take the already disassembled cartridges and submerged them into a vinegar solution. The idea is that the mild acid of vinegar will react with the alkaline limescale and dissolve it into the liquid solution.
After about an hour, I removed the parts and brushed them all down with a basic toothbrush in order to remove any loosened remaining debris. I did however take care not to scratch or score the plastic valves as any scoring would also undermine their ability to form a watertight seal; as this would allow water would pass through the miniscule divots that would be present on the seal’s contacting surfaces.
With regards to this method, I should note that I made exceptions for the rubber parts of the cartridges. The blue o-rings and red/blue rubber gasket. I just did not feel comfortable submerging them in an acidic solution for extended periods. I feared that it may affect the chemistry of the rubber material and ‘dry’ it out. Thus causing it to crack or split; and consequently be no longer effective as a waterproof seal. (FYI the pictures below are lying.)
Testing
After a quick rinse in tap water I decided to reassemble the cartridges and put them back into service for extended testing. Although the leaking was significantly reduced as it didn’t drip continuously as before: it still dripped regularly. This was tested by leaving an empty cup under the tap head overnight. I’d regularly find the typical coffee cup I used at least half-full come morning.
This lead me to surmise a number of scenarios:
1) That the water was making it in between the the plastic valve seals. Likely due to surface scoring caused by either my cleaning/brushing of the valve discs; or the limescale itself being ground into the discs as they operated over the years.
2) Water is making it’s way around the gaskets and o-rings, in addition to bypassing the valves. And that I have only remedied/alleviated one issue.
Greasing the cartridge components
With these conclusions I decided to then purchase some plumber’s grease. Thinking that it would be perfect for the application of assisting the plastic disc valves and rubber gaskets to form water tight seals. The Ebay listing for it explicitly stated just that.
However once the product arrived, I decided that I wouldn’t be testing it’s efficacy as I decided that it was not fit for use. The reason why: was that the little tin came with a whole host of warnings on it’s label. Warnings typically associated with poisonous chemical products.
Particularly the “Do not eat, drink, or smoke …” around this product warning gave me pause. Especially when coupled with the fact that the very vapours from this thing were an irritant. It emitted a vapour that was a mild irritant to the eyes and nose, smelling almost minty like the ointment “tiger balm”.
So despite the labelling assuring me that it is indeed appropriate for use within water faucets, I decided that this was not something that I wanted coming in contact with my drinking water – and ultimately ending up inside me. Maybe I am just paranoid. Maybe not.
Either way if an irritant chemical has warnings not to ingest it, and by using it for it’s intended purpose you are essentially guaranteeing ingestion. Maybe don’t use that chemical. Ultimately, it all just comes down to personal choice, and how much you trust anonymous Ebay sellers over your own intuition.
Personally I just found a substitute: Petroleum Jelly. A non irritant, non toxic chemical that routinely comes in contact with human skin and lips. So chances are good that it won’t do any harm if you accidentally ingest some with your drinking water.
Additionally unlike the plumber’s grease, the jelly can be used with rubbers like the o-rings and gaskets. I used to use some back in school within the science lab. A small amount was applied to the mouth of a bunsen burner’s rubber gas hose in order to help form a gas-tight seal between it and it’s brass attachment. I remember it even hydrating the dry red rubber of those hoses. Although I am pretty sure that petroleum jelly is also flammable so I’m not sure if that was a particularly safe application for it. :/
However within this application: my only concern with petroleum jelly is it’s longevity in the system, and heat resistance. However those are considerably less concerning than putting poison in a drinking tap. So after greasing everything up: the o-rings, the rubber gasket, and the plastic valve discs, then tighten everything down properly – I did note further improvement. Now the faucet barely leaks at all. Barely being the keyword here.
Jobs a gudd’un mate.
Post repair review
I left some time after the repair for observation before writing this review and it seems the leak is slowly returning after a month. A month of constant use keep in mind. I am still chalking it up as a success because this repair really only needed some basic tools and materials. The only consumables used are just household sundries like vinegar and pure petroleum jelly. So it can be done for next to nothing.
There are even more things I could do short of purchasing replacement cartridges, and that would be to use an additional o-ring under the main water ingress rubber gasket. This will put more pressure on the plastic disc valves. Squashing them together to form an even tighter pressure fit seal between them.
Although there are likely drawbacks to this, including and not limited to: firstly, a stiffer tap – the more downward pressure on the cartridge mechanism, the harder it would be to rotate it; and secondly, the higher pressure on the discs themselves would cause them to grind against each other more, and likely shorten their lifespan by promoting scraping of their contact surfaces.
Although if you are repairing it in the first place, chances are that they are already well towards their end-of-life, in which case this fix will extend it couple of months before they likely fail into a unrepairable state. At which point replacing the ceramic discs will be needed. Just my guess.
Closing thoughts
Not much to say here really, I surmised my thoughts on the repair itself within the Post repair review above. So I’ll go with a more personal note here.
I actually enjoyed looking at this tap cartridge more than I thought I would. It really is amazing what people are capable of creating through iterative design and mass production. It reminds me of the gaming concept of min-maxing: of getting the most out of the lest.
I mean look at the simple design and construction of this cartridge. It uses two plastic/ceramic discs to create a watertight seal by just pressing against each other. Undoubtedly the results of iterative cost cutting to the point of being adequate or acceptable, and little more.
I know that when I usually talk about cost cutting, especially when discussing mass produced goods: its usually in a negative light. That’s because the stimuli or catalyst for those tangential rants tends to be a product that is sub par, and in my opinion not fit for purpose. Products that I refer to as “factory fresh e-waste”.
However that is not the case here, these cartridges are fit for purpose. But they are also (in my humble opinion) built down to a price point. One that makes economical sense. Look at the bill of materials here for example: a brass housing and insert, a retaining clip for the insert, a metal washer, two o-rings, a water gasket, a metal screw, two plastic/ceramic discs, and maybe one or two additional miniscule hidden parts that I missed. That is a list that has been reduced to the absolute necessities and little more, but nothing less either. I admire the philosophy honestly.
Anyway, enough gushing about the tap. Since I repaired it: it’ll do that itself in a year or two ;). Upon looking up the Ebay prices for replacements, I noticed that they are very cheap. (At least the generic versions.) The average price for a set of two is £10; and if you wanted to repair your own two cartridges with a kit of replacement o-rings, gaskets, and ceramic discs, then that’ll set you back around £2.50. Very doable.
As a final note, if you found yourself confused as to why I kept referring to the cartridge discs as both made out of plastic and ceramic. Well, this is because the unit I was working on (pictured) felt like plastic to me. A hard somewhat brittle plastic.
However upon looking them up online, apparently they are all ceramic. I also wrote the repair section during the repair process prior to this; and I decided to leave it as plastic because that’s what I felt that material was while I was handling it. Although I am by no means an expert on such things, if the internet says that it’s ceramic then I guess it likely is.
Thank you for reading.