Adds desc to things lacking them.

code/modules/atmospherics/machinery/components/binary_devices/valve.dm

@@ -5,7 +5,7 @@ It's like a regular ol' straight pipe, but you can turn it on and off.
 /obj/machinery/atmospherics/components/binary/valve
 	icon_state = "mvalve_map"
 	name = "manual valve"
-	desc = "A pipe valve"
+	desc = "A pipe with a valve that can be used to disable flow of gas through it."
 
 	can_unwrench = TRUE
 

code/modules/atmospherics/machinery/components/trinary_devices/filter.dm

@@ -1,6 +1,7 @@
 /obj/machinery/atmospherics/components/trinary/filter
 	name = "gas filter"
 	icon_state = "filter_off"
+	desc = "Very useful for filtering gasses."
 	density = FALSE
 	can_unwrench = TRUE
 	var/on = FALSE

code/modules/atmospherics/machinery/components/trinary_devices/mixer.dm

@@ -4,6 +4,7 @@
 
 	name = "gas mixer"
 	can_unwrench = TRUE
+	desc = "Very useful for mixing gasses."
 
 	var/on = FALSE
 

code/modules/atmospherics/machinery/other/zvent.dm

@@ -5,6 +5,7 @@
 	icon_state = "vent_map"
 	density = FALSE
 	anchored=1
+	desc = "This may be needed some day."
 
 	var/on = FALSE
 	var/volume_rate = 800