Just wondering if anyone can help?

On 2 different pumps I changed the diaphragms and these first times round they worked great.
However on changes since then I get leaks out the bottom. I know the new diaphragm is not gripping the bottom of the flange when re-assembling, but there are those 2 screws at the bottom of the unit in the way that you have to deal with whilst pressing against the spring.
I thought using Inox MX6 silicone grease might have taken up any capillary style leaks. Appears I was right on the top side in and out valves and wrong on the main large diaphragms as the grease makes them slip off during assembly.
I've tried reassembling these things more than 5 times now.

I replaced the diaphragm in my TMC foot pump and I seem to recall removing the foot lever whilst reassembly to relieve pressure from the spring. If I recall there was something about the pressure from the spring on the foot lever that made easy reassembly difficult.

Thank you Jolene. I was messing around with that on the 5th rebuild today, but did not figure out how to disconnect the spring successfully on rebuild. I'm all ears if you know how.
Also talked to someone else whom has 3 Whale Gusher foot pumps on board and says that they are quite reliable and are fairly easy to do the diaphragm replacement on. He also said that the Whale Gusher should be good for about 20 years before plastic gives out. He'd not compared them to the TMC though. I'm thinking about changing over. Bugger is that I'd have to build a flat base to connect the Whale type to as the current TMC type connect to the cupboards vertical face.

I think it was a matter of pushing out the pin that the foot lever pivots on. I really can't remember but I can have a look tomorrow when back on board.
I think that the foot lever caused the 2 halves of the pump to misalign and the remedy was to remove the fulcrum pin, drop out the lever,, assemble the pump, then refit the lever and drive the pin back in whilst the lever was mid stroke under some tension.

O.K.
It looked like the pin was not removable. Then again I didn't try real hard to remove it. Will have a look.

I removed the pedal fulcrum pin. It made a big difference to lining up the diaphragms. The pump works a whole lot better now, although it still leaks at the very bottom.
Thank you Jolene.
I remember a friend saying that a trick of manufacturing used to save materials is to slightly fill in moulds to reduce their volume. This may be happening here. I found that the
diaphragms are different depths of around 300 micron. Not that my calipers are high quality, but I didn't move the caliper between measurements.
The side by side photo shows the difference.
--The second backup pump.--
On the second newer backup pump I decided to repeat the process of pin removal and test it, but gave up in the end as I it is just such a fiddle to make the diaphragm line up on he pedal side. Harder than the old one was. I think something has slightly changed in the manufacturing. Also I am looking at the poor quality of spares. I am going to try the Whale Gusher foot pump soon. I'll just put up with these leaky TMC pumps for the moment as they work somewhat well enough.

We can also see that the diaphragm does not reach the plastic base when placed over the lip it's supposed to seal to.




Seal A

Seal B

Very thin at base diaphragm holding point.


Knocking out fulcrum pin.

I'm happy to see you got it apart with the lever off.
There may be a bit of distortion on the sealing faces causing the leak or as you said that the replacement parts don't quite match.
The pump is only made of a soft white plastic and I could quite easily understand how they could distort if way it has been installed allows operational pressure on the lever past the limit of its pumping stroke.
I have two of them on my boat and one that started leaking l rebuilt with no problems. When I bought the service kit I was advised to throw the old pump in the bin and buy a new one but I wasn't going to be defeated that easily .

Well I bought a Whale Galley Gusher the other day. Initially I thought it looked cheap and nasty as reinforcements in moulding looked too thin. However it's said to be a nylon chassis with nitrile for the flexible rubbery bits. The TMC must be a PP (PolyPropyline) which appears superior to PE (PolyEthyline) but still (in my experience) not quite as strong or chemically resistant as Nylon.
wait .... alas I may be wrong on PE compared to PP --> The table on pg 255 of ' Materials for Engineers and Technicians' by Higgins (5th Ed 2010 - ISBN 978-1-85617-769-6) says PE has many characteristics above PP. Although in my historical manufacturing experience I was trying to use EPP (Expanded PP) which seemed to have better impact resistance and shape recovery as it's used in car bumper bars.
Back to Nylon compared to PE - pg 258 of the book above point out that it's density is 1.12 compared to 0.95
Moulded Tensile MPa 60 compared to 30. (although nylon with filaments can be 350MPa)
Thus hopefully the Whale (Munster Simms) hopefully should be tougher and hold shape under load better.
I don't have any data on Nitrile other than my work gloves are nitrile. Super tough and super chemical resistance with a medium of elasticity.
Plastic appears not to be an all encompassing term. PE compared to Nylon compared to PolySulphones or PTFE are not exchangeable terms. They also change drastically when embedded with short filament and even more with long directional filaments. Watching destruction testing vids on YT of different plastics points to a situation where two shapes from the same mould in different plastics are nowhere near the same product.
I think we have been mislead drastically on what plastic means. It used to mean 'Cheap rubbish manufactured out of Asia' to me, however further exploration and research has shown that plastics are superior to natural materials and metals in many (but not all) applications.