How often should a liquid cooling loop be filtered?
The interval is not a date.
Change-out at terminal differential pressure, 35 psid against a 60 psid element maximum
· coolant sample every 50 to 100 days · side-stream at 5–15 % of circulating
volume
Two questions get confused here. One is whether the element is loaded, and the other is whether the
fluid is still in specification. Different answers, different instruments.
We supply the loop between the coolant distribution unit and the cold plate. Neither of those two
parts is in the catalogue.
Side-stream filtration cart · the gauge leg is the
instrument the interval comes from
01 / The side-stream split
Size the split, and the turnover time follows
What the split is for
A side-stream loop diverts 5 % to 15 % of circulating volume from the main header, filters it and
returns it downstream of the take-off. Full-flow inline filtration of the whole volume costs more
energy and a larger footprint, which is why the split exists. The split is a design decision, and it
sets the turnover time.
Worked on a 4,800 L loop
At 10 % of volume per hour that is 480 L/h, a full turnover every 10 hours. Published guidance puts
the practical band at a full turnover every 6 to 12 hours. At 10 % per hour a contaminant slug takes
hours to reach the element, which is why filtration problems arrive slowly.
Take-off, element, return
Loop 4,800 L · 10 %/h = 480 L/h · turnover 10 h · published band
6–12 h
02 / What loads an element
Why two loops of the same volume load differently
Production residue in pipework
Scale and swarf left in pipework and heat exchangers from the build.
Reaches the loop at first fill
Abrasion from pumps
Particles shed by pumps and mechanical components under continuous running.
Continuous while running
Installation and sealing residue
Material left by the assembly and sealing steps, carried into the fluid.
At commissioning
Ageing of the fluid itself
Inhibitor depletion and glycol breakdown raise conductivity and organic
load.
Months, accelerated by heat
Element rating moves the rate too. Bag filtration at 1–10 µm takes the
bulk load, cartridges at 0.5–5 µm do the fine polishing, and a 5 µm element blinds
quickly unless it sits downstream of a bulk stage.
That is why the change-out number is a differential pressure and not a date.
03 / The pressure window
The change-out figure needs the maximum beside it
Differential-pressure window for a PP pleated depth cartridge, and the instrument that reads
it.
Condition
Value
Clean 2 µm element
0.17 bar (2 psid)
Recommended change-out
35 psid (2.4 bar)
Maximum differential
60 psid (4.1 bar) at 20 °C
Cartridge temperature rating
80 °C (176 °F)
Transmitter ranges
±125 Pa · ±500 Pa
Transmitter accuracy
±0.2 % of span
Transmitter resolution
±0.02 % of span
Read at operating temperature
Differential pressure is read at operating temperature, not at fill temperature.
04 / Commissioning sets the load
A loop is cleanest the day it leaves the bench
Commissioning · the day the loop is dirtiest
Free iron from site work
Stainless steel welded, ground or fabricated on site without cleaning and re-passivation to ASTM
A380 / A967 practice leaves free iron in the coolant, and free iron fouls microchannel surfaces.
Glycol that separated under vacuum
A glycol blend can partially separate under vacuum, so a sample after a vacuum fill is the only way
to know the blend is uniform. Entrained air compounds it: degassing works best at temperatures a
loop only reaches under load, so air problems surface weeks after handover.
05 / Coolant quality targets
What the filtration is protecting, as targets
Nine parameters
Loop water-quality targets, labelled for a glycol or facility water loop. Microchannel blockage,
scaling and pitting are the failures the rows guard against.
Parameter
Target
Guards against
Suspended solids, cold plate
< 5 µm
Microchannel blockage
Suspended solids, rear-door HX
< 10 µm
Microchannel blockage
Turbidity
< 1 NTU
Particulate load, optical proxy
pH, glycol or facility water
7.0–9.0
Corrosion and inhibitor effectiveness
Conductivity, glycol or facility water
50–300 µS/cm
Dissolved ionic contamination
Hardness
< 50 ppm
Scaling
Chloride
< 50 ppm
Pitting in stainless steel
Dissolved oxygen
< 2–4 mg/L
Corrosion rate
Microbial
Zero active growth
Biofilm, with biocide residual held
PG25 design basis · 25 % propylene glycol by volume · pH 8.8 · freeze
−11 °C · boil 103 °C
06 / Sampling
Sample on a cadence, from the right point
The cadence and the panel
Every 50 to 100 days
Quarterly fits the same band. The sample is drawn from a hot closed loop,
not from a drain point.
It is the buffering capacity that says how much corrosion protection is
left. A published PG25 fluid carries 1.4 mL 0.1 M HCl.
ICP metals analysis detects trace metals, which is how active corrosion announces itself before a pH
reading moves.
07 / Maintenance schedule
What to write into the maintenance schedule
Change-out · terminal differential pressure for the element in service, not a date
· Sampling · every 50 to 100 days from a hot closed loop · Instrument check ·
differential pressure against a known clean baseline after every element change
Particulate abrasion of a seal face is measured in weeks, and compression set in a seal in months to
years. Filtration state is the one input on that list a maintenance team controls week to week.
EMS-CF-S08Side-stream filtration unit, 8 % divert setpoint
Vessel to 150 psi (10.3 bar); element change-out 35 psid against
a 60 psid maximum.
PDF
EMS-CF-F1-10Pleated depth cartridge, 1 µm absolute, 10 in
PDF
EMS-CF-F5-20Pleated depth cartridge, 5 µm nominal, 20 in
PDF
EMS-CF-FP-DPElement differential-pressure monitor
Catalogued on the window it spans: 2 psid clean to 60 psid
maximum.
PDF
EMS-CF-WQ-CContacting conductivity cell
Cell constants 0.01 and 0.1 cm⁻¹, ranges 0.04 to 1,000
µS/cm.
PDF
EMS-FF-FS60Fill and flush unit, 60 L/min side-stream
PDF
Send the loop volume, the current element rating, the differential pressure and the last
sample result, and the reply sizes the element from those four figures.
08 / Specification sheet
Send the loop volume and the element rating
Ask for the specification sheet
The reply returns the specification sheet, the dimensional drawing and the datasheet for the code,
inside one working day.
