Heinke Merlin DH reg info?

[Fibonacci]

Morning vintage team…
I have just been given a Heinke Merlin DH reg from a former marine biologist now retired and downsizing his household.
He used to use it as his primary regulator back in the day so I’d like to restore it back to working order.
Trouble is while I’ve successfully restored a couple of Nemrod Snarks, various Spiros and RAMs I don’t know where to start with the Heinke Merlin!
Any tips or leads for parts or overhaul kits gratefully received

 

[John C. Ratliff]

The CG-45 website has a full description, with diagrams, for this regulator.

Double Hose Regulators - Heinke (Siebe-Heinke)

SeaRat

 

[Fibonacci]

Thanks @John C. Ratliff I also found some service info on the VDH manuals archive.
The more I delve into these Merlins the better I like them!

The MKVI had a lot of modern refinements and was designed to be modular to accept a reserve assembly, surface supply hose on a banjo bolt (so it could be oriented as required), HP gauge, externally adjustable IP vs shims and it seems they were made into the 1970's.
Its definitely the one to have, but I will learn on the MKV!

A spare plated brass surface supply port blank off plug (which is BSPP Port G3/8-19) could be drilled and tapped for a SAE-3 ORB port to accept standard 3/8-24 UNF hoses for my MKV... hmm... possibilities.

Quick update on progress...
Paint stripper, Citric Acid pickle, ultrasonic cleaning in Simple Green Crystal 1:20 made a big improvement!

The plunger type HP gauge originally connected to the G1/8 HP port actually cleaned up very well, just needed a new -006 90 o-ring!

O-rings
So far the two main Reserve Housing o-rings appear to be AS568 -112 90
The Reserve Plunger is close to a AS568 -007 90 but unsure if its just been distorted over time... its as hard as a rock!
Erik's O-ring Calculator however gives a -007 o-ring a pass based on the bore diameter, piston diameter and o-ring groove details... so will give that a try.

The OPV seal is a moulded plug, quite perished now so measuring it up and drafting drawings for possible reproduction. The Venturi Seal is a custom size, so also measured.

The Merlin MKVI at least seems to have quite a following in the UK, so hopefully someone has kicked off some reproductions?
Rather than reinvent the wheel @iain/hsm do you have any UK contacts that may possibly have Merlin spares?
Any leads much appreciated...

Duckbill
From what I can find on CG-45 it seems the reason the main exhaust valve on the Heinke MKV was placed in the hose near the can vs inside the can was to evade the original Siebe Gorman patents, since changed to the more usual position on the MKVI when Heinke was taken over by SG.
Looking at parts drawings of the MKV and MKVI it seems the internals of the can were very similar, and a modern reproduction silicone rubber duckbill will fit once the original crimped brass inner tube has been removed.
I can see why they introduced an inner support spring on the MKVI.
Clears the diaphragm standoffs too...

 

[Fibonacci]

The reserve mechanism is quite an 'elegantly simple' design...
It is present on most MKV's I've seen but not common on the MKVI's usually being blanked off.

When the tank is full the plunger is compressed allowing full air volume to the diver

When tank pressure drops to 300psi, a small groove in the seat still allows some air to pass giving the diver an indication air is low.

When the reserve lanyard is pulled, the plunger moves to the stop pin allowing the remaining air to be used at full volume.

 

[Fibonacci]

The Merlin regulator is a pretty clever concept from the golden era when Britain was an innovation powerhouse (the Spitfire, Land Rovers, Mini, Jet engines etc). I imagine slide rules and Proper Yorkshire tea sipped out of chipped enamel mugs

There are some deliberate design decisions inside the body such as the smooth dish shaped depression that makes me think the air bleed past the LP Tilt Valve stem was well accounted for. The inner surfaces leading to the intake horn have been smoothed and rounded like a gas-flowed cylinder head!
Maybe they had some original Merlin V12 influence on their namesake?

The clearance around the slot for the Tilt Valve stem is larger than it really needs to be, so its either for achieving the correct volume of air delivered to the case vs directed up the Venturi and/or to allow 1-2 degrees of rotation of the Venturi Tube and slightly adjust the distance to the LP Diaphragm rub plate?

The spherical end of the LP Tilt Valve fits closely into a corresponding spherical recess in the body... no springs required. The square edged recess is for a sealing washer to the Venturi Tube.
So air pressure holds it up in place, I imagine the reg would hiss for a second or two when first pressurised?

When depressurised it drops back slightly from the 7 deg seat in the Venturi Tube.
This also has the benefit of no excessive engraving of the LP seat over time... this LP seat was unmarked after decades stored in a hot shed!