Updates canister process() to use atmos helper procs

code/ATMOSPHERICS/_atmospherics_helpers.dm

@@ -29,8 +29,6 @@
 	if (source.total_moles < MINUMUM_MOLES_TO_PUMP) //if we cant transfer enough gas just stop to avoid further processing
 		return -1
 
-	//var/source_moles_initial = source.total_moles
-
 	if (isnull(transfer_moles))
 		transfer_moles = source.total_moles
 	else
@@ -69,6 +67,40 @@
 
 	return power_draw
 
+//Gas 'pumping' proc for the case where the gas flow is passive and driven entirely by pressure differences (but still one-way).
+/proc/pump_gas_passive(var/obj/machinery/M, var/datum/gas_mixture/source, var/datum/gas_mixture/sink, var/transfer_moles = null)
+	if (source.total_moles < MINUMUM_MOLES_TO_PUMP) //if we cant transfer enough gas just stop to avoid further processing
+		return -1
+
+	if (isnull(transfer_moles))
+		transfer_moles = source.total_moles
+	else
+		transfer_moles = min(source.total_moles, transfer_moles)
+
+	var/equalize_moles = calculate_equalize_moles(source, sink)
+	transfer_moles = min(transfer_moles, equalize_moles)
+
+	if (transfer_moles < MINUMUM_MOLES_TO_PUMP) //if we cant transfer enough gas just stop to avoid further processing
+		return -1
+
+	//Update flow rate meter
+	if (istype(M, /obj/machinery/atmospherics))
+		var/obj/machinery/atmospherics/A = M
+		A.last_flow_rate = (transfer_moles/source.total_moles)*source.volume //group_multiplier gets divided out here
+		if (A.debug)
+			A.visible_message("[A]: moles transferred = [transfer_moles] mol")
+
+	if (istype(M, /obj/machinery/portable_atmospherics))
+		var/obj/machinery/portable_atmospherics/P = M
+		P.last_flow_rate = (transfer_moles/source.total_moles)*source.volume //group_multiplier gets divided out here
+
+	var/datum/gas_mixture/removed = source.remove(transfer_moles)
+	if(!removed) //Just in case
+		return -1
+	sink.merge(removed)
+
+	return 0
+
 //Generalized gas scrubbing proc.
 //Selectively moves specified gasses one gas_mixture to another and returns the amount of power needed (assuming 1 second), or -1 if no gas was filtered.
 //filtering - A list of gasids to be scrubbed from source
@@ -400,4 +432,17 @@
 	var/output_volume = (sink.volume * sink.group_multiplier) + sink_volume_mod
 		
 	//get the number of moles that would have to be transfered to bring sink to the target pressure
-	return pressure_delta*output_volume/(air_temperature * R_IDEAL_GAS_EQUATION)
+	return pressure_delta*output_volume/(air_temperature * R_IDEAL_GAS_EQUATION)
+
+//Calculates the APPROXIMATE amount of moles that would need to be transferred to bring source and sink to the same pressure
+/proc/calculate_equalize_moles(datum/gas_mixture/source, datum/gas_mixture/sink)
+	if(source.temperature == 0) return 0
+	
+	//Make the approximation that the sink temperature is unchanged after transferring gas
+	var/source_volume = source.volume * source.group_multiplier
+	var/sink_volume = sink.volume * sink.group_multiplier
+	
+	var/source_pressure = source.return_pressure()
+	var/sink_pressure = sink.return_pressure()
+	
+	return (source_pressure - sink_pressure)/(R_IDEAL_GAS_EQUATION * (source.temperature/source_volume + sink.temperature/sink_volume))

code/ATMOSPHERICS/components/binary_devices/passive_gate.dm

@@ -80,7 +80,7 @@
 				transfer_moles = min(transfer_moles, calculate_transfer_moles(air1, air2, pressure_delta, (network2)? network2.volume : 0))
 		
 		//pump_gas() will return a negative number if no flow occurred
-		returnval = pump_gas(src, air1, air2, transfer_moles, available_power=0)	//available_power=0 means we only move gas if it would flow naturally
+		returnval = pump_gas_passive(src, air1, air2, transfer_moles)
 	
 	if (returnval >= 0)
 		if(network1)

code/game/machinery/atmoalter/canister.dm

@@ -8,6 +8,7 @@
 
 	var/valve_open = 0
 	var/release_pressure = ONE_ATMOSPHERE
+	var/release_flow_rate = ATMOS_DEFAULT_VOLUME_PUMP //in L/s
 
 	var/canister_color = "yellow"
 	var/can_label = 1
@@ -175,21 +176,15 @@ update_flag
 			environment = loc.return_air()
 
 		var/env_pressure = environment.return_pressure()
-		var/pressure_delta = min(release_pressure - env_pressure, (air_contents.return_pressure() - env_pressure)/2)
-		//Can not have a pressure delta that would cause environment pressure > tank pressure
+		var/pressure_delta = release_pressure - env_pressure
 
-		var/transfer_moles = 0
 		if((air_contents.temperature > 0) && (pressure_delta > 0))
-			transfer_moles = pressure_delta*environment.volume/(air_contents.temperature * R_IDEAL_GAS_EQUATION)
+			var/transfer_moles = calculate_transfer_moles(air_contents, environment, pressure_delta)
+			transfer_moles = min(transfer_moles, (release_flow_rate/air_contents.volume)*air_contents.total_moles) //flow rate limit
 
-			//Actually transfer the gas
-			var/datum/gas_mixture/removed = air_contents.remove(transfer_moles)
-
-			if(holding)
-				environment.merge(removed)
-			else
-				loc.assume_air(removed)
-			src.update_icon()
+			var/returnval = pump_gas_passive(src, air_contents, environment, transfer_moles)
+			if(returnval >= 0)
+				src.update_icon()
 
 	if(air_contents.return_pressure() < 1)
 		can_label = 1