You are here: Home > Marine Product Guides > Pump System Guides

Direct Cooling

It should be noted that engine manufacturers pay special attention to the design of engines for direct cooling in order to minimise corrosion in the cooling passages. However many small craft owners marinise standard car engines successfully.

Raw water (river or seawater) is pumped directly through the cylinder block, exhaust manifold, exhaust silencer (if fitted) and exhaust pipe. To ensure efficient engine performance it is essential that an optimum operating temperature is being maintained by regulating the amount of cooling water through the cylinder block, either using 'Manual' or Automatic temperature control.

Manual Temperature Control

A hand valve is fitted in parallel to the engine block. When the engine is cold, the valve must be opened to reduce the flow of water through the block. As the engine temperature increases, the valve is closed gradually until optimum temperature is maintained.
IMPORTANT. Do not regulate the pump flow by fitting the by-pass valve between the pump discharge and suction or by restricting either the pump discharge or suction.

Automatic Temperature Control

A Marine thermostat is fitted after the cylinder block and is closed when the engine is cold allowing most of the cooling water to be pumped via a spring loaded back-pressure valve to the exhaust. As the engine temperature increases, the thermostat opens until the required operating temperature is maintained.

Heat Exchanger Cooling

A pump recirculates Fresh Water on a closed circuit through the cylinder block, thermostat and around the tubes of a heat exchanger (Primary Cooling Circuit) which is often an integral part of the vented expansion - or header tank. Cold Raw Water is pumped by a second pump through the heat exchanger tubes (Secondary Cooling Circuit) and maintains the fresh water in the primary circuit at an average temperature of 80-90oC.

Keel Cooling

Keel Cooling is basically the same as heat exchanger cooling, except that the fresh water is recirculated through the keel cooling pipes which are fitted outside to the bottom of the boat. The heat generated by the engine is dissipated directly to the raw water flowing around the pipes.

Raw Water Cooling

Raw water cooling systems demand a great deal from circulating pumps. They must have the unfailing ability to self prime at various engine speeds and must be able to pass such solids as sand and silt without impairing the pump's flow.
On average, petrol engines and fast running diesel engines require a raw water pump flow of approximately 8-8½gpm (36-39l) for each 100BHP for Direct Cooling systems and 14½-15½gpm (65-70l) for each 100BHP for Heat Exchanger Cooling systems.

Correct Incorrect
1. Install electric self-priming pumps as low as possible, consistent with a dry, ventilated and accessible location.
1 Correct 1 Incorrect
2. Keep suction pipework as short and straight as possible. Use reinforced hose that will not deform or collapse under suction conditions. Ensure that all connections are airtight.
2 Correct 2 Incorrect
3. Keep pipework simple. Complex valving in the suction system increases the risk of air leaks and loss of priming ability.
3 Correct 3 Incorrect
4. Use pipes of internal diameter at least as large as the nominal bore of the pump ports.
4 Correct 4 Incorrect
5. Always fit an adequately sized suction strainer to protect the pump from debris. Make sure that it is accessible, and remember to inspect it periodically.
5 Correct 5 Incorrect
6. Remember that small electric submersible pumps are rarely useful at more than 1.2m (4ft) vertical discharge head. Medium/large submersibles are similarly ineffective above 2m (7ft).
6 Correct 6 Incorrect
7. Always fit a manually operated bilge pump as a back-up to electric or engine-driven pumps.
7 Correct 7 Incorrect

These simple actions will only take a short while to carry out, they may save you a lot of money.

When you leave your boat for the winter, to avoid frost damage, drain your pressurised water system.

The easiest way is to turn the pump off, open the taps and allow the water to drain out, then, open the drain valves to empty the rest. If your system doesn't have drain valves, disconnect a pipe joint at the lowest point in the system and allow to drain.
It may also be necessary to drain the pump supply tank and hot water storage tank separately.

Before you leave check you have drained as much water as possible.

If your system is frozen and you find it in this state check everything. Pumps can crack, water storage heaters can split, pipe can split, joints can break. If you are using Hep2O then the pipe should be undamaged, it is however not uncommon for a joint to split.

Do not turn on your pump until you are confident there are no leaks in the system. You may pump the contents of your freshwater tanks into the bilge, if your bilge pumps are frozen this may have knock-on effects.

Troubleshooting a Pressurised Water System

Insufficient pressure or flow:

Check the pump is running correctly and in the right direction.

Is the correct size pipe installed for the size of pump? We do not recommend using smaller pipe bore than the bore of the pump ports.

Check for blockages in the pipework.

Check the pump specification, is the pump large enough for your system?

Check the pipework layout, are there restrictions or is the layout over complicated? Could you or should you consider a larger pipe size? Larger vessels and longer pipe runs can often benefit from larger bore pipe particularly for main runs and up to showers.

Motor runs but no flow:

Check the pump is priming -

Is there water in the tank? If there is no water the pump can't generate pressure so it won't turn off.

Are there any air leaks in the suction line? Check all joints.

There may be an airlock in the inlet line, ensure there is a steady gradient to the pump without any dips.

Check for closed valves in the inlet or blocked pipes.

Check the valves in the pump (or the venturi) are not blocked, dirty or damaged

Motor runs hot:

Motor is overloading - check the fuse size, check the motor condition

The pump maybe cavitating due to a blocked inlet - check/clear the inlet pipe

The pressure switch cut-out is set too high and the pump can't reach the pressure - check and reduce the pressure if required.

Pump wont turn off:

Voltage is low at the pump - check the voltage at the pump, if it's low check the batteries, check the wire size and cable run against the pump specification

Water tank is empty - check/refill the tank

Blocked orifice in the pressure switch - clear the blockage or replace the switch

Blocked or worn jet pump impeller

Airlock resulting from lack empty water tank


 Click to enlarge... UNITED STATES Alcon Solenoid Valve Catalogue
ALCAT 11/09

English (6.0 Mb)

 Click to enlarge... EUROPE Alcon Catalogue


 Click to enlarge... INTERNATIONAL Industrial Pumps & Valves Catalogue (English)
IPAC 01/10

Introduction (3.1 Mb)
Centrifugal Pumps (11.9 Mb)
Diaphragm & Drum Pumps (8.1 Mb)
Flexible Impeller Pumps part A (8.7 Mb)
Flexible Impeller Pumps part B (3.0 Mb)
Gear Pumps, Hand Pumps & Lobe Pumps (7.4 Mb)
Chemical Resistance Guide (0.9 Mb)

 Click to enlarge... INTERNATIONAL Beverage Product Catalogue

English (6.8 Mb)

 Click to enlarge... INTERNATIONAL Jabsco Flexible Impeller Wine Brochure
ENG: 950-0663

Engish (7.8 Mb)

 Click to enlarge... INTERNATIONAL Jabsco Flexible Impeller Food Brochure

English (8.0 Mb)

 Click to enlarge... INTERNATIONAL Flexible Impeller Pumps Brochure

English (1.4 Mb)

 Click to enlarge... INTERNATIONAL Flojet Motor Operated Diaphragm Pump Brochure
F100-407 (MPU)

English (0.6 Mb)

 Click to enlarge... INTERNATIONAL Industrial Superior Solutions Brochure
ENG: 43011-0007

English (1.8 Mb)
French (6.1 Mb)
Spanish (0.8 Mb)

 Click to enlarge... EUROPEAN Wind and Water Powered Generator Brochure

English (3.2 Mb)

 Click to enlarge... INTERNATIONAL Marine Trade Catalogue

Company Profile (0.1 Mb)
Contents (0.1 Mb)
New Products (1.2 Mb)
Introduction (0.4 Mb)
Toilet Systems (1.7 Mb)
Water Pressure Systems (1.6 Mb)
Bilge Pumping Systems (4.2 Mb)
Livewell/Baitwell Pumps (1.1 Mb)
Transfer Pumps (1.2 Mb)
General Purpose Pumps (1.4 Mb)
Ventilation Blowers (0.3 Mb)
Searchlights (1.1 Mb)
Flexible Impeller Pumps (5.5 Mb)
Impeller Replacement (2.6 Mb)
Service parts (13.3 Mb)
Index and Conversions (1.0 Mb)

 Click to enlarge... INTERNATIONAL Marine Product Brochure

English (2.0 Mb)
French (2.2 Mb)
Dutch (2.4 Mb)
Danish (2.1 Mb)
Italian (2.1 Mb)
German (2.1 Mb)
Polish (13.0 Mb)
Portuguese (2.1 Mb)
Spanish (2.1 Mb)
Swedish (2.1 Mb)

 Click to enlarge... INTERNATIONAL RV Pumps & Accessories Catalogue

English (3.2 Mb)

 Click to enlarge... INTERNATIONAL Oil & Gas System Engineering Capabilities Brochure

English (7.1 Mb)

 Click to enlarge... INTERNATIONAL Oil & Gas Short Brochure

English (3.9 Mb)

 Click to enlarge... INTERNATIONAL Hygienic Rotary Lobe and Flexible Impeller Pump Catalogue

English 43011-0006 ENG (4.3 Mb)
German 43011-0006 GER (4.3 Mb)
Spanish 43011-0006 SP (0.8 Mb)

 Click to enlarge... INTERNATIONAL Jabsco/Xylem Pureflo Pharma Brochure

English (0.8 Mb)

Terms and Conditions of Sale

N. American Terms and Conditions of Sale (0.2 Mb)

Terms and Conditions of Sale

Midland-ACS and Alcon EU Conditions of Sale (0.2 Mb)

EU Terms and Conditions of Purchase

EU Terms and Conditions of Purchase (0.2 Mb)

US Terms and Conditions of Purchase

US Terms and Conditions of Purchase (0.2 Mb)