diff --git a/devices.lua b/devices.lua
index d9edcad..6dd9617 100644
--- a/devices.lua
+++ b/devices.lua
@@ -165,13 +165,7 @@ for s in ipairs(states) do
 	})
 
 	-- FIXME: this currently assumes that pumps can only rotate around the fixed axis pointing Y+.
-	-- TODO: these directionality functions should be behind a helper so the fountainhead can use something similar.
-	local upwards = {x=0,y=1,z=0}
-	local neighbourfn = function(node) return { upwards } end
-	local directionfn = function(node, direction)
-		return vector.equals(direction, upwards)
-	end
-	new_flow_logic_register.directional(pumpname, neighbourfn, directionfn)
+	new_flow_logic_register.directional_vertical_fixed(pumpname, true)
 	local pump_drive = 4
 	if states[s] ~= "off" then
 		new_flow_logic_register.intake_simple(pumpname, pump_drive)
diff --git a/pressure_logic/flowable_node_registry_install.lua b/pressure_logic/flowable_node_registry_install.lua
index 3cd9c4d..d8f945b 100644
--- a/pressure_logic/flowable_node_registry_install.lua
+++ b/pressure_logic/flowable_node_registry_install.lua
@@ -52,6 +52,20 @@ register.directional = function(nodename, neighbourfn, directionfn)
 	regwarning("directional", nodename)
 end
 
+-- register a node as a directional flowable that can only flow through either the top or bottom side.
+-- used for fountainheads (bottom side) and pumps (top side).
+-- this is in world terms, not facedir relative!
+register.directional_vertical_fixed = function(nodename, topside)
+	local y
+	if topside then y = 1 else y = -1 end
+	local side = { x=0, y=y, z=0 }
+	local neighbourfn = function(node) return { side } end
+	local directionfn = function(node, direction)
+		return vector.equals(direction, side)
+	end
+	register.directional(nodename, neighbourfn, directionfn)
+end
+
 
 
 local checkbase = function(nodename)