Air leak ...valve on middle tank?

[Fuzz]

Seems like F gauge goes down pretty fast actually both go down close to same.Valve on middle tank is leaking where the two parts are joined,try to tighten 4 screws are tight.I assume this is PPV. Although there are two valve gizmos on tank.The leaking one is much bigger than the other.Will try to post a pic of the one leaking where two parts are joined.Can this gizmo be rebuilt or new one  the way to go.Can't show the pic.This thing is about 4" overall high.has a 3/4 inch +-  diameter 3inch tall cylinder on top.The smaller valve? has a red cap like device on it Sorry about no pic.

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[Scrap]

Top one is the pressure-check for your air dryer.  It is going to drop F tank some pressure as it uses that and supply tank air to regen the dryer.  But it shouldn't leak external though. https://www.anythingtruck.com/product/650-S4341003100.html

Bottom one is pressure protection for an accessory. Can't see too well but kinda looks like it?  Might need to chase its male threads as they die cast the threads as part of the valve, giving you a parting line down the middle of the threads that'll grow small bubbles.  There are a million different versions of them so look for a 223-something stamped on it.  That'll tell you what it is.  223-585-2 genuine (not a x-ref) at a KW dealer will be chased threads already w/ 1/4 NPT females both ends.  At least it used to be...  For a generic pic of valve ->  https://www.anythingtruck.com/product/810-032219.html

[Fuzz]

Thanks  Scrap,You nailed it as usual...appreciate you taking the time...the large one Pressue check for Air dyer is leaking at seam where top and bottom screw togheter...Thanks again