Reverse rotation of the pump
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During a routine inspection at work yesterday, it was found that one of the backup hot oil pumps was rotating in reverse continuously, even though the motor was not powered on. After opening the coupling cover, it was observed that the speed of rotation in reverse was still very low. Upon investigating the cause, it was discovered that the preheating valve of the backup oil pump was set too wide open (almost fully open), which caused the fluid to flow in the opposite direction. After closing the small valve and the hot-line hand valve, the pump reversal phenomenon disappeared. These are some small things I experienced while operating, which I would like to share with all fellow sailors.
This is a normal phenomenon; if the rotation speed is too high, it may prevent the system from functioning properly
Also, if the pump reverses too quickly, it can not only affect the flow rate of the pump in operation, but in severe cases it can even cause the impeller of the pump to come off! !
A fast reversal speed can damage the pump. This is also one of the reasons why check valves are commonly installed at the pump outlet. It seems that design and operation are equally important for the stable operation of equipment
I did similar tasks when I first started working. For the pre-heating line of hot oil pumps, a dual-valve setup is generally recommended, as it makes it difficult to handle the pump once one of the valves wears out；
I’ve encountered this situation as well, but it was caused by the outlet valve of the backup pump not being closed properly. We shared a check valve between the two pumps, and we made modifications later on
It’s best to check, as reverse rotation of some pumps not only affects the seals but also the tightness of the bolts
We have also encountered similar problems; the main reasons for pump reversal are as follows: 1. The motor reverses direction when its connections are reversed. 2. The pump outlet valve is open, and backflow of the medium causes the pump to rotate in reverse. 3. The preheating valve is open, and backflow of the medium causes the pump to rotate in reverse.
In our previous 200,000-ton atmospheric and vacuum distillation unit, the feed oil pump did not have check valves; if there was high moisture content or a power outage, the pump would rotate in reverse, and in severe cases, the pump body would leak. After installing the check valve, release it.
When the standby pump is in hot standby mode, it is necessary to control the opening degree of the warm-pump valve to ensure that the goal of warming the pump is achieved without causing the pump to run in reverse. Otherwise, it will cause the back nut to loosen, which may lead to serious failures after the pump is started. This is not a normal phenomenon; adjustments must be made. Such issues require special attention during routine inspections.
This is a normal phenomenon; a standby pump, while in its normal standby mode, needs to operate its pre-heating element at a reduced level in order to maintain low-speed operation in reverse (especially for heavy hot oil pumps). . . :lol
We’ve encountered this problem many times! Fortunately, the outlet pressure isn’t high; if it were high, things would get serious, as the bolts could loosen due to reverse rotation, and the pump might even get damaged! ~
I have also encountered this situation; generally, it occurs when the opening degree of the preheating valve is too large at the start of preheating. At that time, the temperature of the fluid inside the pump is low. After preheating for a while and the temperature rises, the standby pump begins to rotate in reverse. Therefore, it is necessary to conduct more thorough inspections during the initial stage of preheating of the standby pump, to carry out more frequent shaft turning operations, and to adjust the opening degree of the preheating valve.
When this phenomenon occurs frequently, the opening degree of the preheating valve requires empirical judgment
We also often encounter such situations, especially with crude oil pumps (gear pumps)
I’ve encountered this too: I increased the setting for the pre-heating line of the hot oil pump without realizing that it might cause the pump to run in reverse, and then left. It wasn’t until I returned at the next scheduled time that I noticed both pumps were running; upon inspection, it turned out that the pre-heating setting had been set too high. Reversal of rotation of the pump in this device is a common occurrence, but no damage to the pump has been observed yet
I’ve heard this claim for the first time, but it does make sense – it saves the hassle of turning the shaft by hand