diff --git a/scada-common/util.lua b/scada-common/util.lua
index 8dffd40..38cfc1f 100644
--- a/scada-common/util.lua
+++ b/scada-common/util.lua
@@ -80,6 +80,33 @@ util.adaptive_delay = function (target_timing, last_update)
     return util.time()
 end
 
+-- TABLE UTILITIES --
+
+-- delete elements from a table if the passed function returns false when passed a table element
+--
+-- put briefly: deletes elements that return false, keeps elements that return true
+---@param t table table to remove elements from
+---@param f function should return false to delete an element when passed the element: f(elem) = true|false
+---@param on_delete? function optional function to execute on deletion, passed the table element to be deleted as the parameter
+util.filter_table = function (t, f, on_delete)
+    local move_to = 1
+    for i = 1, #t do
+        local element = t[i]
+        if element ~= nil then
+            if f(element) then
+                if t[move_to] == nil then
+                    t[move_to] = element
+                    t[i] = nil
+                end
+                move_to = move_to + 1
+            else
+                if on_delete then on_delete(element) end
+                t[i] = nil
+            end
+        end
+    end
+end
+
 -- MEKANISM POWER --
 
 -- function kFE(fe) return fe / 1000 end
diff --git a/supervisor/session/rtu/txnctrl.lua b/supervisor/session/rtu/txnctrl.lua
index 3d74484..2d6be2e 100644
--- a/supervisor/session/rtu/txnctrl.lua
+++ b/supervisor/session/rtu/txnctrl.lua
@@ -66,22 +66,7 @@ txnctrl.new = function ()
     -- close timed-out transactions
     public.cleanup = function ()
         local now = util.time()
-
-        local move_to = 1
-        for i = 1, public.length() do
-            local txn = self.list[i]
-            if txn ~= nil then
-                if txn.expiry <= now then
-                    self.list[i] = nil
-                else
-                    if self.list[move_to] == nil then
-                        self.list[move_to] = txn
-                        self.list[i] = nil
-                    end
-                    move_to = move_to + 1
-                end
-            end
-        end
+        util.filter_table(self.list, function (txn) return txn.expiry > now end)
     end
 
     -- clear the transaction list
diff --git a/supervisor/session/svsessions.lua b/supervisor/session/svsessions.lua
index 88c57cd..d0b76cc 100644
--- a/supervisor/session/svsessions.lua
+++ b/supervisor/session/svsessions.lua
@@ -1,5 +1,6 @@
 local log = require("scada-common.log")
 local mqueue = require("scada-common.mqueue")
+local util = require("scada-common.util")
 
 local coordinator = require("supervisor.session.coordinator")
 local plc = require("supervisor.session.plc")
@@ -99,22 +100,10 @@ end
 -- delete any closed sessions
 ---@param sessions table
 local function _free_closed(sessions)
-    local move_to = 1
-    for i = 1, #sessions do
-        local session = sessions[i] ---@type plc_session_struct
-        if session ~= nil then
-            if session.open then
-                if sessions[move_to] == nil then
-                    sessions[move_to] = session
-                    sessions[i] = nil
-                end
-                move_to = move_to + 1
-            else
-                log.debug("free'ing closed session " .. session.instance.get_id() .. " on remote port " .. session.r_port)
-                sessions[i] = nil
-            end
-        end
-    end
+    local f = function (session) return session.open end
+    local on_delete = function (session) log.debug("free'ing closed session " .. session.instance.get_id() .. " on remote port " .. session.r_port) end
+
+    util.filter_table(sessions, f, on_delete)
 end
 
 -- PUBLIC FUNCTIONS --