Jiwei Fork Liquid Level Switches Widely Used in Level Measurement for Crude Oil Storage Tanks
Jiwei Fork Liquid Level Switch is widely used for level measurement of crude oil storage tanks. It is very welcomed by its customers because of its stable and reliable performance. People may be wondering why Jiwei Fork Liquid Level Switch is so well recognized and trusted by our customers. Let´s check it out by analyzing technical requirements for level meters under the working conditions for crude oil storage tanks, comparing similar products in the market with Jiwei Fork Liquid Level Switch and the technical advantages of Jiwei Fork Liquid Level Switch.
１. Technical requirements for level meter in working conditions for crude oil storage tanks
As an important storage unit in the oil refining industry, crude oil storage tanks are widely used in the petrochemical industry. According to the regulations in 《National safety supervision bureau: Notice on Further Strengthening the Safety Management in the area of Chemical storage Tanks》(No.86, 2014)，for crude oil storage tanks, it is necessary to not only install continuous level meters such as radar level meter, differential pressure transmitter etc., but also install liquid level switches for overfill alarm or dry run alarm.
Take the oil tanks in the storage tank area in crude oil pipeline transportation station as an example, two level switches shall be installed on the external wall of each tank for overfill and dry run alarm respectively. At the same time, these level switches and electric valves on the input & output pipelines of the storage tank constitute an interlock protection system. When crude oil is injected into a storage tank and the level of the oil reaches to a designated high level, the level switch for overfill alarm will send out an alarm signal and the interlock protection system will turn off (close) the electric valve on the input pipeline of the tank. When crude oil flows out of the storage tank and the level of the oil reaches a designated low level, the level switch for dry run alarm will send out an alarm signal and the interlock protection system will turn off (close) the electric valve on the output pipeline of the tank.
Flammable, explosive and adhesion are typical characteristics of crude oil. Therefore, the selected liquid level switches firstly must meet explosion-proof qualification, secondly must be tolerable to material buildup to some extent. When the level switch used for crude oil storage tanks misses alarming points or makes false alarms, it will greatly increase the risk of crude oil leakage due to overfill and risk of pump damage due to dry run. High reliability becomes a fundamental requirement for the selected liquid level switch in order to avoid malfunction of the level switch for level control of crude oil storage tank.
２. Comparison between various liquid level switches
There are many types of liquid level switches. Float liquid level switch, capacitive liquid level switch, external attached liquid level switch and fork liquid level switch are the most commonly used liquid level switches. In the following table, we show the comparison between these common liquid level switches.
Comparison table for common liquid level switches
|
Level switch |
Measuring principle |
Features |
Ex. protection |
Price |
|
Float liquid level switch |
A magnetic float in Float Liquid Level Switch moves up or down with the liquid level. When it reaches to the designated position, it triggers reed switch nearby to send out a switching signal. |
Simple structured, easy to use and the float often stuck. |
Meet flameproof enclosure explosion protection |
low |
|
Capacitive liquid level switch |
It is based on detecting changes of capacitance between the probe and the wall of the tank. The capacitance is related to the volume of the liquid in the tank. It is small when the tank is empty while it is much bigger when the tank is full. The instrument sends out a switching signal by detecting the changes of the capacitance. |
Tolerate slight material buildup, strong corrosion resistance, but difficult to calibrate and poor accuracy. |
Meet explosion protection requirements for both intrinsic safety and flameproof enclosure |
Moderate |
|
External liquid level switch |
Variable frequency ultrasonic technology is used to achieve non-contact liquid level measurement. The probe emits ultrasonic waves and detects the residual vibrating signal on the wall of the tank. When the liquid level rises to the detecting area of the probe, the amplitude of the residual vibrating signal becomes smaller and triggers a switching signal. |
Not necessary to stop operation for cleaning the tank. But installation is quite demanding. False alarm happens due to losing data. |
Meet explosion protection requirements for both intrinsic safety and flameproof enclosure |
High |
|
Fork liquid level switch |
Piezoelectric devices are used for driving the vibration of the fork body and detecting the changes of the vibration. When the fork body comes into contact with the measured material, the resonance frequency is reduced significantly. The changes of the vibration frequency will be detected by a piezoelectric device. The detecting circuit will identify the changes and send out a switching signal. |
Not affected by media properties, simple installation, no calibration and maintenance required, no wear and tear, Tolerate slight material buildup |
Meet explosion protection requirements for both intrinsic safety and flameproof enclosure |
Moderate |
From the comparison table above we can see that when float liquid switch is used, the float is often stuck in its moving path because of high viscosity of crude oil and results in failure. It is a kind of low valued consumable in the automation industry. For capacitive liquid level switch, problems caused by material buildup happen repeatedly. Its sensitivity has to be adjusted according to the specific dielectric constant and it is difficult to adjust. Also its measuring accuracy is lower. Comparably non-contact external liquid level switch does not have problems stated above. But when the liquid surface fluctuates too much, the echo signal is easily disturbed and the instrument is quite expensive as well. It is not effective to be used in this application overall. Fork liquid level switch is designed in an integrated structure without any moving parts. Problems such as parts stuck will not happen to it and its performance will not be affected by waving of the liquid surface. Furthermore it can be used right after the installation. It does not need to be calibrated.
３. Characteristics and advantages of Jiwei Fork Liquid Level Switch
The reason why Jiwei Fork Level Switch can be widely used for crude oil storage tanks is because of its following characteristics and advantages:
1) Compared with float level switch and capacitive level switch, fork liquid level switch is more tolerable to material buildup.
2) Compared with other fork liquid level switches in the domestic market, Jiwei Fork Liquid Level Switch has more redundancy to material buildup and it is less prone to false alarms.
Many of our customers doubt the ability of fork liquid level switches to tolerate material build up. For example, a customer in an oil company in Xinjiang mentioned that the company has tried a fork liquid level switch from another domestic manufacturer for the crude oil storage tank and false alarms due to material buildup had happened. Further communicating with the customer, we found that the fork liquid level switch the customer selected is a fork level switch that aimed for both solid and liquid medium level measurement. Its fork body is about 100mm long and There are technically trade-offs in its design so that the instrument can be used for both solid and liquid medium level measurement. In addition, its fork body is not precisely tuned for resonance, the power consumption is high and safety of the instrument is low. Further, it cannot tolerate slight material buildup and inevitably make false alarms.
Jiwei Ring-11 Fork Liquid Level Switch is different from the instrument stated above. Its fork body is only 40mm long and two fork bodies are completely identical after being precisely tuned to achieve complete resonance. The measurable medium density can be as low as 0.5g/cm3. Jiwei Ring-11 has higher redundancy for material buildup to avoid false alarms.
3) Jiwei Ring-11 Fork Liquid Level Switch meets explosion protection requirements for both Intrinsic Safety (Ex ia IIC T6) and Flameproof Enclosure (Ex d IIC T6). It is safe and reliable to operate, especially suits for level measurement applications in the petrochemical industry. Jiwei Ring-11 is a dependable choice for level control in petroleum and petrochemical fields.
According to the feedback from our customers in a few petrochemical companies in Xinjiang petrochemical group, Jiwei Ring-11 Fork Liquid Level Switches perform well in level measurement for crude oil storage tanks. The instruments have been reliably working and never had false alarms since they were installed.