In the water treatment system of the petrochemical industry, the medium filter is a key link to ensure
that the subsequent process water quality meets the standard. It intercepts impurities such as crude oil
residue and rust in the water through the filter material, and the drain valve is the impurity discharge
channel of the filter. Failure can cause the filter material to harden and the filtration efficiency to decrease,
which may indirectly affect the stable operation of downstream heat exchangers and reactors.
First, understand how media filters "intercept" impurities in petrochemical water?
To solve the problem of sewage discharge, the first step is to clarify the working principle of the media
filter. Its core is "filter material adsorption+water flow infiltration". Through reasonable filter material
matching and water flow design, efficient interception of impurities can be achieved:
Core components: The media filter usually consists of a tank body, a filter layer (commonly quartz sand,
anthracite, etc.), an inlet device, an outlet device, and a drain valve, among which the filter layer is the
key to filtration;
Water flow direction: In petrochemical systems, the water to be treated usually enters from the top of the
filter and penetrates the filter layer uniformly from top to bottom;
Filtering process: When water penetrates the filter layer, large impurities in the water will be intercepted
by the upper layer of filter material with larger particle size (such as anthracite); Medium sized suspended
solids will be captured by the middle layer of quartz sand; Small particles will be adsorbed by the high-density
filter material in the lower layer, and finally clean water will be discharged from the outlet device at the
bottom of the filter;
The necessity of sewage discharge: As filtration continues, impurities will gradually accumulate on the
surface and inside of the filter material layer, causing pore blockage of the filter material and an increase
in pressure difference between the inlet and outlet of the filter. It is necessary to regularly discharge the
ccumulated impurities through the sewage valve in order to restore the filtering capacity of the filter.
Key point: Does the drain valve not discharge? The 5-step troubleshooting method effectively solves
the problem
01 Sort out 'operational errors' first
Many times, if the drain valve does not operate, it is not due to equipment damage, but rather a deviation
in operation or parameter settings. Prioritize these two basic checks:
Confirm the open status of the drain valve: If it is a manual valve, check if the knob is turned to the "open"
position; If it is an automatic valve, check if the control panel accidentally touches "manual lock" or if the
timed discharge parameters (such as interval and duration) are set incorrectly to ensure that the valve has
indeed received the "open" command;
Check the operation process: In some scenarios (such as after backwashing the filter), it is necessary to first
close the backwash valve and then open the drain valve. If the process is reversed, it may cause no water
flow at the drain outlet, and the equipment operation procedures need to be followed again.
02 Check the 'pressure value'
The normal operation of the drain valve depends on the system pressure drive. If the pressure is abnormal,
even if the valve is opened, it cannot drain. It is necessary to focus on checking:
Standard pressure range: The normal operating pressure difference of medium filters in the petrochemical
industry is usually 0.05-0.15MPa. If the pressure difference is too low, it is necessary to check whether the
upstream feedwater pump is outputting normally or whether the inlet valve of the filter is not fully opened
(insufficient water flow power can cause impurities to not be pushed to the drain valve);
High pressure treatment: If the pressure difference exceeds 0.2MPa, it indicates that the filter material has
been severely blocked. It is necessary to first release the pressure according to petrochemical safety regulations
before conducting subsequent investigations.
03 Disassemble the "valve core"
The discharge valve of the medium filter is exposed to petrochemical water containing impurities for a long
time, and the valve core and sealing ring are easily blocked or corroded by impurities. Before disassembly,
perform "power-off and pressure relief":
Check the valve core: After disassembling the drain valve, observe whether the valve core is attached with
filter debris or rust. If there are impurities, rinse it with clean water; At the same time, check whether the
valve core has scratches or deformation. If it is damaged, replace it with a stainless steel valve core of the
same model (resistant to petrochemical wastewater corrosion);
Check the sealing ring: Check if the sealing ring is aged or cracked. It is recommended to replace it with a
fluororubber material sealing ring (oil resistant, corrosion-resistant, suitable for petrochemical working conditions).
04 Road Intersection "
Blockage of pipelines or valve ports is a common reason why drain valves do not discharge, especially in
petrochemical systems where there are many impurities, which can easily accumulate at pipeline bends
and valve port gaps
Check the sewage pipeline: observe whether there is scaling or bulging on the outer wall of the pipeline,
open the sewage flange at the end of the pipeline, and blow it with compressed air of 0.2-0.3MPa to blow
out the accumulated impurities inside the pipeline;
Clean the gap between the valve port: Use a fine brush to lightly brush the connection port (valve port
sealing surface) between the drain valve and the pipeline to avoid impurities getting stuck in the valve
port. At the same time, be careful not to scratch the sealing surface (otherwise it may cause valve leakage).
05 Check "Control Logic"
If the drain valve is an automatic valve (electric/pneumatic), it is necessary to collaborate with the electrical
or self-control team to investigate the control link and avoid "signal interruption":
Electric valve inspection: Check if the motor power cord is loose; If the motor does not respond, it is
necessary to check whether the gearbox is stuck due to lack of oil;
Pneumatic valve inspection: Check if the air source pressure reaches 0.4-0.6MPa (normal working pressure
of the pneumatic valve), and if the solenoid valve is leaking or blocked; After the power is turned off, the
solenoid valve can be disassembled and the internal impurities can be blown away with clean compressed air.
Advance prevention: 4 daily measures to reduce the recurrence of pollution discharge failures
01 Regular manual sewage discharge
Manually open the drain valve once every 1-3 months (30-60 seconds each time until the discharged water
becomes clear). Automatic drain may have "dead corners", while manual drain can flush out residual impurities
in the pipeline through larger water flow, avoiding valve core blockage;
02 Install Y-shaped filter
Install a Y-shaped filter at the front end of the drain valve to intercept large particles of impurities in the
water in advance and reduce the impurity load on the drain valve;
03 Special maintenance for automatic valves
Check the gearbox oil level of the electric valve every 6 months; Check the sealing of the pneumatic valve
every 3 months and clean the solenoid valve every 6 months to ensure stable power supply;
04 Regularly replace filter media
When the pressure difference between the inlet and outlet of the filter continues to exceed 0.2 MPa, or the
turbidity of the effluent exceeds the standard, the filter material should be replaced in a timely manner.
When replacing, the filter material should be packed in the order of "high-density filter material at the bottom,
low-density filter material at the top", and after packing, backwash 2-3 times until the effluent is clear.
In petrochemical water treatment, the "efficient filtration" of the medium filter and the "smooth discharge" of
the drain valve complement each other. Understanding the principle is necessary to accurately diagnose faults,
and troubleshooting according to the process is necessary to effectively solve problems. Daily prevention is
necessary to reduce recurrence.
