Thank you Fabio.........i found this thread from the beginning with the Regner pump very interesting...
Disappointingly the Regner pump disappeared with the commercial ownership of the company
The pump from Herrmann Echtdampf raised new hope, however it too has lost membership experiences :WN
regards Derek
Is there nothing new :BT with this thread since October 2018?...... :pok: ......Derek
Hans, I agree any round head socket ...Tork head or variant screw is not scale like. It is also acknowledged that the forged head and rolled thread in a comparable steel provide a higher mechanical strength over machined screw format
However these are cosmetic only......from the images provided by Thomas....I guess the screws in the steam side are M2??....so if the pump can be proved to be reliable....the original screws can easily be replaced with hex head bolts, or studs & nuts
Following on from this and if sales increase, Thomas may suggest to the manufacturer ''Herrmann'' to change the bolting format 
Derek
Thomas.......the auto translator :M can sometimes mis or change text or intent
This is interesting, however no explanation as to what was defective with the original pump. Did the manufacturer explain the issue?
As Roland notes, the only real way to understand the efficiency of the pump is in a real world test....say boiler @ 50% full and at relief valve pressure......then set the pump to refill the boiler against this boiler pressure
Time the process and let us know the results
Derek
The pressurization of fluids suffer from Hysteresis ......this is more pronounced when short stroke & high velocity [speed of stroke] occurs
In our case here, ever with a perfect flooded suction, essentially it is the lag time between the opening and closing of the check valves that distorts the calculated volume [or lessens the theoretical displaced volume of fluid]
When this is understood, it becomes clear why this phenomena effects short stroke pumps more than long stroke piston displacement pumps
Time is also an element in the calculation...so the higher the speed, the greater the hysteresis effect on the sealing of the check valves
Some reading below :BT ............... Derek
Greetings Thomas.....from Derek in Australia
I am building a steam engined paddle wheeler ...the steam plant is multi national...a Japanese Saito Y2DR twin horizontal engine [12 x 20] with Scottish boiler....lubricator & flanges from Winfried Niggle.....some Chinese from Jin....plus many home built parts
The Regner boiler feed pump was very interesting [before the reported operating issues] and this is how I found this thread and the great progress you have made in a short time period
On of the interesting points with the Hermann pump is Nylon/Delrin components that do not require an oil lubricator....saying this, I understand the natural lubricity or wet steam at say 2 Bar and am surprised that his steam regulator is also OK without oiled steam
I do not see an issue with the exhaust steam in your video......
I am also a member of a number of World wide model boat/steam engine WEB groups, and the group most interested in boat/steam/steam water pump is the French group as below ... a number of their members trialed the Regner pump without success.....I believe they are are not aware of the Hermann Echtdampf pump. Would you mind if I posted a message on their pages with a link back to your thread here?......after all we are similar members of model steam with an interest in a functional steam driven boiler water feed pump
I also attach an image of my build...[having difficiulty,....will post message & see if I can edit with the image]
regards Derek
Thanks Thomas ....a very interesting discovery of a new alternate functional steam driven boiler makeup water pump
We note from your comments that you have a displacement lubricator on the steam supply and your mention of the telephone call to the manufacturer, and we see this lubricator in your photo image
Simply, could you please confirm the ISO Grade of steam oil you are using?
This is an important point as most/many small marine steam engines use ISO 460 Grade oil
regards Derek
