Fuel valves, does other use them?

[magnemoe]

I have for some time used an smart method for cutting off flow from upper stages, this is useful if you want to launch mostly empty tanks, typicaly tankers, fuel depots or miners but also huge interplanetary ships you prefer to refuel in orbit, this can also be done with spaceplanes cheaply if you don't use mining but you need rockets to get your Jool mothership in orbit.

If you launch empty tanks its best to fill them with fuel and use the fuel on the way up, this cut down the dry mass, an S3-14400 tank has a dry mass of 10 ton you have to lift, if you use it for storage its free. This also require that you need fuel left for the upper stage, if you want to put an empty tank in orbit you don't need to cut off fuel, however if the tank is part of an ship or simply have small engines to circulate and some mobility in orbit you need to cut the flow.

Excample

This is an 18 man ship with 50 ton fuel, 53 ton dry mass, 4500 m/s dV and life support for 1000 days.

Notice the relative small lower stage with 1.5 huge tank, its smaller than the spaceship.

This cut off valve is the secret, fuel level in spaceship reach it minimum i trigger it, the fuel flow from spaceship through the strut and too the lower stage, ejecting it cut off the flow.

I can still use the LV-N on the upper stage.

[SofusRud]

or, you could, you'know, disallow the fuel in the tank by right clicking.

[Renegrade]

I have for some time used an smart method for cutting off flow from upper stages, this is useful if you want to launch mostly empty tanks, typicaly tankers, fuel depots or miners but also huge interplanetary ships you prefer to refuel in orbit, this can also be done with spaceplanes cheaply if you don't use mining but you need rockets to get your Jool mothership in orbit.

I used to do something similar for launching large refuel stations, but I don't bother valving it, I just let the fuel lines break when it's time to stage.

The station ends up in orbit with whatever fuel I was able to save for it.

I rarely put up super-massive fuel stations though anymore, so it's been a while since I've used that technique...

[Pthigrivi]

You used to be able to make them action group toggleable with docking ports. Is that no longer possible?

[timsfitz]

or, you could, you'know, disallow the fuel in the tank by right clicking.

Yeah I was going to say that.

[magnemoe]

or, you could, you'know, disallow the fuel in the tank by right clicking.

It would also kill fuel flow to the LV-N outside of the 360 m/s in the 45 liter tanks, you will also get an offset between fuel and oxidiser as you can not disable both at once.

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You used to be able to make them action group toggleable with docking ports. Is that no longer possible?

yes in this setting I could have just used the docking port and disabled fuel flow, its kind of an bad example.

The miner with a core with no fuel but fuel lines inn and four side tanks would be an better example as it has an engine in center and no docking port, here disabling the tanks would not work as you will use lots of time disabling four tanks. Design here was simply to reach orbit, transfer some fuel to LV-N tug who took it to Minmus where it landed and start mining for fuel.