Overheating of Power Units
+ Overheating of Power Units – system leakage
Oil temperature above 55°C should be avoided. Otherwise, the efficiency of the pump drops considerably and its lift is reduced. Aging of the oil is also accelerated.
Possible Causes of overheating
1. Up leveling too long due to the leveling speed being too slow or the slow-down switch being set too low.
2. Machine room's ventilation is inadequate.
3. The frequency of operation is too high for the normal rate of heat dissipation.
As a temporary measure to avoid overheating of the oil resulting in the shut-down of the elevator, the down speed can be slowed to reduce frequency of operation until a permanent solution is installed.
a. If the degree of overheating is not excessive and it takes. For example, two to three hours for the oil temperature to rise from 20°C to 55°C, it may be sufficient to improve air circulation around the power unit. For example, through the installation of a 0.05 kW to 0.10 kW ventilator extracting air out of the machine room or through a fan of similar power, blowing air over the power unit.
b. Should the above be inadequate, depending on the size of the elevator, it will be necessary to install a 10 ~ 50 l/min. Pump to circulate the hot oil through an air cooled radiator of about 0.1 to 0.2 fan kW. It is also essential that there is sufficient extraction of warm air out of the machine room or that the cooler is ourside of the machine room. i.e. in the elevator shaft. The effective cooling power of an air cooled radiator should not to be confused with the power of the fan drive hich normally need only be 0.1 kW or 0.2 kW. Normarlly, the effective cooling power of a cooler power of a cooler need only be approximately 1/4 of the main hydraulic elevator motor, in the case of submersible drives.
Cooling system for the above purpose should be switched into operation when the oil reaches 30 ~ 35°C.
System Leakage (re-leveling)
The aim of manufactures of hydraulic elevator control valves is to produce valves with zero leakage. Due to fine contamination in the oil perfect sealing between valve parts may not always be achieved, leading to a slow down leak of the elevator.
It would become unnecessarily expensive to strive for perfect sealing in every valve in operation. Therefore, because code requirements assure a safe re-leveling system whether descent of the car is caused by valve leakage or through the cooling of the oil in the cylinder pressure system, a minor leakage of the control valve can be tolerated.
1. The European code EN 81-2 require: that the loaded elevator does not leak downwards by more than 10 mm in 10 minutes. This is the standard used to determine if a valve should be serviced for leakage.
2. For practical reasons, a quicker method for judging valve leakage is to close the ball valve in the cylinder line and observe the gauge showing pressure in the cylinder chamber of the valve. If this pressure falls to zero in less than 20 seconds, it may be necessary to service the valve, depending on the diameter of the main ram and sensitivity of the customer.
3. Down sinking giving the impression of leakage can be due to cooling of the oil.
When the elevator is at rest and the temperature of the oil falls, contraction of the oil in the cylinder and piping causes the car to sink. This sinking is very slow but overnight without re-leveling could amount to as much as half a meter, depending on the temperature drop of the oil and the volume of oil in the cylinder system. The elevator re-leveling system, operating normally however, keeps the car at floor level.
4. In the case of control valve, see link indicating where valve down leakage can occur.