Power Unit Overheating
Power unit overheating – system oil leakage
Oil temperatures above 55°C must be avoided. Otherwise the pump efficiency drops considerably and its service life is shortened. The service life of the oil is also rapidly shortened.
Possible causes of unit overheating:
1. The levelling speed of upward levelling is too slow, or the slowdown switch is set too low so that levelling takes too long
2. Insufficient ventilation of the machine room
3. The number of operations is more frequent than the normal rate at which heat can escape.
Temporary solution
As a temporary measure to avoid overheating of the oil in an elevator that is not running, the downward travel speed can be reduced to prevent frequent operation until a complete solution is found and fixed.
Cooling system
a. If the overheating is not excessive, for example if the oil temperature rises from 20°C to 55°C over 2–3 hours, the air circulation around the power unit can be improved. For example, this means installing a 0.05 kW to 0.10 kW ventilation fan to extract the machine room air to the outside, or a similar blower fan.
b. If the above is insufficient depending on the size of the elevator, it is necessary to install a 10–50 l/min pump that circulates the hot oil through an air-cooled radiator with a fan of about 0.1–0.2 kW. It is also important to extract the hot air from the machine room, and the cooler should be outside the machine room, for example in the elevator hoistway (shaft).
The effective cooling power of an air-cooled radiator must not be confused with the power of the fan drive (usually only 0.1 kW or 0.2 kW is needed). In general, for a submerged motor, the effective cooling power of the cooler needs to be at least about 1/4 of the capacity of the main hydraulic elevator motor.
When the oil reaches 30–35°C, the cooling system must operate for the above purpose (see our oil coolers).
System oil leakage (re-levelling)
The manufacturing goal for hydraulic elevator control valves is to make the valves leak-free. Even if there is a perfect seal between the valve parts, it cannot always stay sealed because of fine contaminants in the oil and slowdown leakage of the elevator car.
Achieving a perfect seal in the operation of every valve would cause unnecessary excessive cost.
Therefore, because the code requirements guarantee a safe re-levelling system (whether the car's descent is due to valve leakage or to oil cooling in the cylinder pressure system), slight leakage of the control valve is not a problem.
1. EN 81-2 requirement: if there is no leakage, a loaded elevator must not sink more than 10 mm in 10 minutes. This is the basic check to decide whether the valve needs service because of leakage.
2. As a practical check, a faster way to determine valve leakage is to close the ball valve in the cylinder line and check the gauge showing the pressure in the cylinder chamber of the valve.
If the gauge pressure drops to 0 within 20 seconds, the valve may need to be repaired, depending on the diameter and sensitivity of the main ram.
3. If the car sinks, you may feel that leakage is the cause, but it may also be due to the oil cooling.
When the elevator is on standby and the oil temperature drops, the car may descend because of the contraction of the oil inside the cylinder and pipes. The sinking is very slow, but if a day passes without re-levelling, it can amount to almost 0.5 m depending on the oil temperature drop and the temperature and volume of the cylinder system.
The elevator re-levelling system operates normally, but the car keeps the floor level.
4. The link (Korean) explains at which locations in the control valve leakage can occur.