1 · Your system

Fills in a 40 gpm hydraulic unit with ISO VG 46 oil, cooled by 85 °F water.

What are you cooling?

Sets a typical oil grade. You can change it below.

What cools it?

Water (water-oil cooler) Air (fan cooler, air-oil)

Your numbers

Oil flow through the cooler

Pump flow, or the return-line flow that goes through the cooler.

How hot the oil runs (going into the cooler)

The hottest oil temperature you want to allow. Hydraulics: often 120–140 °F.

Oil temperature coming out of the cooler

same unit

Usually 10–20 °F cooler than the oil going in. Don’t know? Use “More options”.

Oil grade

The ISO VG number on the drum or in the manual (ISO 3448 viscosity grade).

Water temperature going in

same unit

Use the warmest water, or the hottest summer air, you expect.

More options: other ways to get the heat load, result units

How do you want to work out the heat load?

From oil temperatures in and out (default) I know the heat load Estimate from pump motor size (rule of thumb)

Heat load

From the maker, a heat survey or a previous cooler.

Pump motor size, and share that turns into heat

%

Rule of thumb: AKG suggests 25% of input power for most hydraulic power units (40 hp unit = 10 hp heat load). Use a measured value if you have one.

Show results in

2 · Your answer

Where the number comes from: Maker rating printed in the maker’s table · Chart read read from the maker’s chart · Calculated ±20% calculated from published geometry (±20%). Extra capacity = how much more the cooler can do than you need. ±7% AKG A-series: the maker’s chart scale and gridlines disagree, so read these as ±7%.

Confirm with the maker’s sizing software before purchase. These are estimates from catalog data; oil thickness, dirt build-up, water flow and altitude change the real number.

Show all matching coolers

Ranked by smallest extra capacity that still covers the load (smallest adequate margin), not by brand.

Contact the manufacturer or their distributor to confirm sizing before ordering. Each row links the maker’s catalog page and official website.

Technical details for this result

3 · Can I swap to a brazed plate cooler?

For a cooler that is shell-and-tube today. Brazed plates are small and cheap but less forgiving.

Quick estimate (3 questions) Thorough check (every question, cited checklist)

Where does the cooling water come from?

Seawater and salty water attack the copper brazing.

Any known water problems?

Opens the matching water-test questions below.

Highest oil pressure at the cooler, including spikes

Most copper-brazed units are rated about 30 bar (435 psi).

Hottest oil temperature

°C

Do you rod or brush out the water tubes today?

A brazed plate can only be cleaned with chemicals, never rodded.

More questions: water test, strainer, cold start, mounting

Chlorides in the water

mg/L

From a water analysis.

Ammonium (NH₄⁺) in the water

mg/L

Water temperature coming out

°C

Chloride limits get tighter as water gets hotter.

Strainer on the water inlet (1 mm or finer)

Cold-start bypass or relief valve on the oil side

Cold, thick oil can over-pressure a plate cooler.

Coldest oil at start-up

°C

Exposed to freezing (idle, outdoors, unheated)

On/off water valve or water hammer

Cooler held by a bracket (not hanging on the pipes)

Aluminium or galvanised parts in the water loop

Full checklist with sources

Words, method & sources

Glossary

Heat load: the heat the cooler must remove, in hp, kW or BTU/h.
Temperature gap (ETD, entering temperature difference): oil temperature going in minus water (or air) temperature going in. The bigger the gap, the smaller the cooler.
Extra capacity (margin): how much more the cooler can remove than you need, at your flow and temperatures.
ISO VG: oil viscosity grade per ISO 3448; the number is the oil thickness in cSt at 40 °C.
Brazed plate (BPHE): stainless plates brazed together with copper; compact, cannot be opened or rodded.
Shell-and-tube: oil around a bundle of water tubes inside a shell; tubes can be rodded out.
Rule of thumb: engineering practice, not a maker limit.

How it works: formulas, fits, correlations

Heat load Q = ρ · V · c_p · (T_in − T_out), with oil properties at the mean oil temperature. Viscosity comes from the ISO VG grade (ISO 3448, kinematic viscosity at 40 °C) through the ASTM D341 (Walther) chart equation, assuming a viscosity index of about 100. Density, specific heat and conductivity use the Cragoe petroleum-oil correlations (US NBS Misc. Pub. 97). The pump-power option is a rule of thumb (AKG: about 25% of input power).
ETD = oil inlet temperature − coolant (water or ambient air) inlet temperature. Cooler capacity is taken as proportional to ETD at a given oil flow, the selection method AKG and Emmegi publish; for other makers it is a rule of thumb.
Maker rating: a number printed in the maker’s table (Bowman, Emmegi, Parker SWO). Single-point ratings are used only from 70% to 100% of the rated oil flow (rule of thumb) and scaled by ETD.
Read from maker chart: AKG curves were digitized from the vector PDF charts and fitted (q = Q / (A + B·Q), median fit error 0.4%); Parker PWO curves were read by eye from chart images (about ±3% of full scale). Flows outside the printed curve are excluded. On the AKG A-series chart the printed y-axis labels (about 29.0 pt per doubling) do not line up with the plotted gridlines (27.8 pt per doubling); A-series values use the midpoint of the two readings, capped at 6% above the label reading, and are shown as ±7%.
Calculated from published geometry (±20%): HYDAC HEX S brazed plate units, from the plate dimensions and plate pitch in the HYDAC catalog, using the Martin (1996) chevron-plate correlation (VDI Heat Atlas N6), ε-NTU counterflow, ISO VG 46, oil in 60 °C, water in 20 °C, water flow half the oil flow. Assumed (not published): 60° chevron angle, area enlargement 1.17, 0.4 mm plates, port bore from thread size. Without any fitting, the same method predicted AKG/P ratings with 6.9% mean error (90% within 13%) and Parker PWO ratings with 12.5% mean error (90% within 20%) above an oil Reynolds number of 20; lower flows are left out.
Not included: Bosch Rexroth AB32-09 (table values not yet verified against the PDF), oil-side pressure drop, altitude and fan-speed corrections, and fouling allowances.
Swap check limits are quoted from the makers’ water-quality and installation documents listed below; items marked rule of thumb are engineering practice, not a maker limit.

Sources

Manufacturer websites (for sizing confirmation and local distributors)

AKG Thermal Systems (akgcoolers.com) · EJ Bowman (ej-bowman.com) · Emmegi (emmegi.group) · Parker Hannifin (parker.com) · HYDAC (hydac.com)
Brazed plate and swap-check sources: Alfa Laval (alfalaval.com) · SWEP (swepgroup.com) · Danfoss (danfoss.com) · Thermal Transfer Products (thermaltransfer.com)

Catalogs and references

AKG Thermal Systems: A, H, HR, HD, HDZ, C, DCSB and AKG/P brazed plate catalogs (PDF)
EJ Bowman hydraulic oil coolers catalogue (PDF)
Emmegi MG shell & tube heat exchangers (PDF)
Parker (Olaer) SWO shell & tube water/oil cooler (PDF) and PWO brazed plate water/oil cooler (PDF)
HYDAC plate heat exchangers, E 5.815 (PDF)
Alfa Laval, Brazed and gas-to-liquid plate heat exchangers instruction manual, 200001565-4 (PDF) · Alfa Laval CB60 product leaflet (PDF)
SWEP, Recommendations regarding water for BPHEs (PDF) · SWEP B25T product sheet (PDF)
Danfoss, Guideline of water quality for copper brazed plate heat exchangers (PDF)
Thermal Transfer Products EK Series (PDF) (shell-and-tube viscosity and pressure-drop guidance)
H. Martin, “A theoretical approach to predict the performance of chevron-type plate heat exchangers”, Chemical Engineering and Processing 35 (1996) 301–310; VDI Heat Atlas, 2nd ed. (Springer, 2010), ch. N6.
R. K. Shah and D. P. Sekulic, Fundamentals of Heat Exchanger Design (Wiley, 2003): ε-NTU relations and plate geometry definitions.
S. Kakac, H. Liu and A. Pramuanjaroenkij, Heat Exchangers: Selection, Rating and Thermal Design, 3rd ed. (CRC Press, 2012), ch. 10.
ASTM D341, viscosity-temperature charts for liquid petroleum products; ISO 3448, industrial liquid lubricants: ISO viscosity classification; C. S. Cragoe, Thermal properties of petroleum products, US NBS Misc. Pub. 97 (1929).

Oil cooler & heat exchanger sizing