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N18 and N75 question.

990 views 9 replies 5 participants last post by  adam-  
#1 ·
I know these are more or less the same thing (or at least look so from the outside) but perform slightly different functions and are slightly different on the inside (or are they?) Is it that one is vacuum and the other is air,or are they both the same in this respect?

Also does their at-rest position always allow an air path from say the input to output 1 but not output 2,and then when energised from the input to just output 2 and not output 1? So basically they're just on/off or open/closed air change over valves?

I need a quick and cheap air change over valve in the next day or so and if an N18 or N75 will work,I can easily get one at my local scrappie tomorrow.
 
#2 · (Edited by Moderator)
When I've messed with my N75 is passes positive pressure (turbo created) to the actuator, to open the waste gate. I am unsure of the reference port function, as that goes into the TIP.

In my mind the device could have had two ports not three...

The electrical connection is a simple PWM dictating how much pressure passes through to the actuator.

I have no idea re internal construction.

:)
 
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#4 ·
Ok thanks guys.I've since worked out that a simple change over valve won't work anyway.When you pressurise one side of a pneumatic actuator to make it move in one direction,you then have to de-pressurise that side before you can make it move in the other direction.Lego and a VW fuel flap release actuator to the rescue!
 
#8 ·
I guess the N75's TIP port is to bleed off pressure from the actuator port so the wastegate has a "closing" response. This bleed being different for the various valves, H, J, E/F. The reason why some valves lead to boost spikes on some setups.

:)
 
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#9 · (Edited by Moderator)
n75 could still work on your pneumatics. your pressured air to the bottom port. then connect each port to each connection on the actuator. as its changes over it will use the pressured air to help open/close it
Yes Royce,but if I understand what you're saying,you still need to vent the pressurised side of the piston down to atmospheric pressure BEFORE you can pressurise the other side to make it move the other way.

A normal change over valve won't do this.It can be done with a change over valve and two normally closed valves to do the venting,or four normally closed valves like this can do it (I only bought two of these as that's all I thought it would need).....

_57_zpsbquglo2v.jpg

Four of those complicates it quite a bit though as it needs extra relays etc,a normally open position that allows one side to stay pressurised by default would be a lot better.
 
#10 ·
That's down to the response time due to the N75 DC. Apply full current to it and it'll jam open irrespective of the version. You get boost spikes because the map is expecting that a certain DC will give a certain boost, basically.

N75 wouldn't work, it doesn't seal on one side.