Comparision of Mamod/MSS/PPS Reverser Valves

Lner fan Sam · Post by **Lner fan Sam** » Sun Mar 24, 2013 7:03 pm

What is the adhesion like on mamod loco?

dougrail · Post by **dougrail** » Mon Mar 25, 2013 11:11 pm

Hmm. On Swordbreaker v1, I observed it liked reversing better than forward...!!!! [fresh from building, Jan 2012 onwards]

This was with DS supercyls and a PPS reverser though. O.o

Sadly I cannot see if I can replicate this as I am now on SB v2.2 with the new cylinders, of which I've found near balanced performance i rev and forward - and forward has provided a couple of excellent performances sofar.

The full boiler would act as a weight - but maybe it's the distance the steam has to travel through the system from boiler to being exhautsed-out?? [if that makes sense]

laurence703 · Post by **laurence703** » Tue Mar 26, 2013 4:14 pm

Adhesion depends on how much added extra's you've put on it also what mods its got and the usual rail conditions, weather and what you've got behind it...
For their size they can shift a fair load though

dougrail · Post by **dougrail** » Sun Mar 31, 2013 7:04 pm

Having got bored, and a little frustrated with the current patient [however am due to test new springs....claws crossed...] I took a good look at the actual construction of a Mamod/MSS rotor and block.

For one thing, there's a reason why the slots are one side rounded and one side 'pointed'...and that pointed set of ends is on the left side - where the steampipe from the dome is.

If you try and round those pointed ends out as I had mistakenly, naively in my defence, suggested, it will allow steam to enter the rotor regardless of what position the rotor is in. Cleverly, the PPS one's steam-channel, although rounded, are shorter in length, allowing 'shut off'.

Just a heads up.

Chris Cairns · Post by **Chris Cairns** » Sun Mar 31, 2013 9:02 pm

The original Mamod reverser/regulator valve was actually thought out quite well with the gradual opening of the straight sided slots, but the overall width of the slot was too big (particularly when operating above the original design pressure of 1 Bar), and of course it was cheaply (and thus poorly) constructed.

The PPS (now RWM) one would have never been fitted to a standard Mamod SL operating at 1 Bar, so the smaller width of the slots allows for the increase in pressure that the modified Mamod SL would have been operating at. Whilst the slots are smaller in length than the Mamod one the 4 holes in the PPS block have been chamfered.

We still have had no further contributions with experience of using a PPS/RWM reverser/regulator valve in an unmodified Mamod SL/MSS without a cab mounted regulator.

Chris Cairns.

dougrail · Post by **dougrail** » Sun Mar 31, 2013 9:40 pm

I could do a bit of temporary surgery...?

Chris Cairns · Post by **Chris Cairns** » Sun Mar 31, 2013 9:57 pm

Do you still have the bits for an unmodified Mamod SL (i.e. the old 1 bar safety valve, not the later 25 or 40 PSI ones, and standard pipework - no cab mounted regulators)?

I previously tried it in my Mamod SL3 so I do not think it will be any different in my MSS kit built loco.

Chris Cairns.

dougrail · Post by **dougrail** » Mon Apr 01, 2013 1:32 am

I have a Mamod loco which is boiler > steam dome > rev block for the steam, original cylinders and original brass boiler with sight glass fitting. Alas all I have is 25psi sv's.

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Comparision of Mamod/MSS/PPS Reverser Valves

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