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28th May 1971, Page 51
28th May 1971
Page 51
Page 51, 28th May 1971 — road and
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Which of the following most accurately describes the problem?

workshop by Handyman

3enchwise: Cool it (3)

ROBLEMS with fans occur mainly round the drive belt and pulleys, and ispection on well-used engines should take the clearance between the inner face of le belt and the bottom of the pulley V—in ther words, the belt must not "bottom" in ie V, otherwise the drive provided by the 'edging grip of the V is lost. With certain ldustri al machines such as fork-lift trucks se radiator is at the rear and the fan drives ir past the engine from the opposite end of le truck.

Under certain conditions—dusty floors, :c—the rear side of the radiator core can ecome choked with a mixture of oily dust r mud, and can cause serious overheating roblems. Inspection should look out for and it may be necessary to have :..gular steam cleaning on the core to keep ir passages clear.

2ressurized zone

Another important item is the radiator ap. Although it merely appears to be a pring-loaded cap for reasons of security, its rue purpose is not always clearly undertood by the trainee. What this type of cap oes, firstly, is to make the cooling system to a lightly pressurized one, even though aere is a visible overflow pipe vented to tmosphere. To achieve this, the filler cap onsists of two valves, a pressure valve at he bottom and a vacuum valve at the top, oth in line with the overflow pipe. The itention is to permit a light pressure to luild up within the system for the purpose if raising the boiling point without any loss if coolant.

Quite a low pressure is needed to achieve his, the pressure valve being usually set to Ipen at 4 psi. Thus any sudden overheating hat raises the system pressure above 4 psi vill cause the valve to open, letting out team or coolant until the valve closes again, thereby controlling overheating.

The vacuum valve is designed to deal with the situation when the engine cools, and the pressure inside the engine falls below that on the outside, ie. below atmospheric pressure, as otherwise hose pipes or thin-walled items could collapse. As it is, the vacuum valve is forced open by the 14.7 psi outside, air enters via the overflow pipe and the pressure equalizes inside and outside the system.

Tight joints Radiators intended to work as pressure systems arc specially stiffened to withstand pressure, and these systems . need good hoses and tight joints to operate successfully. As vehicle shapes change shorter and wider cooling surfaces may have to be provided behind front grilles. But now with the radiator water level below that in the engine, the system has to be pressurized, and an additional tank is found on many systems to act as an overflow or expansion tank. Earlier versions of the overflow tank were positioned high but now quite a few are mounted much lower, and sometimes some distance from the main radiator. All is well so long as they are properly sealed and strongly piped.

In operation, any pressure rise or overheating will force the temporarily surplus coolant out of the main system, along the pipe to the overflow tank; as the engine cools down and the pressure falls below atmospheric pressure the water in the overflow tank will return to the radiator. Therefore this system can handle quite severe operating conditions with no loss of water at all. It should be remembered, however, that there is a pressure release valve in the overflow tank, and a slack fan belt or blanking off could cause water loss from this valve.

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