There are many types of accessories for boiler auxiliary equipment, and we should pay attention to all safety accessories and valves whether they are working properly under the premise of ensuring quality, because they are the main accessories that control the operating parameters of the boiler and are very important. Common boiler safety accessories and valves include: pressure gauges, water level gauges, safety valves, high and low water level alarms, sewage devices, etc.

No matter which safety accessory or valve is abnormal, it will cause damage to the operation of the boiler. Therefore, clarifying the causes and solutions of boiler safety accessories and valves failure is very important for boiler safe and stable operation.

Through years of theoretical accumulation and on-site practice, EPCB has summarized boiler safety accessories and valve failures, causes and solutions to help your boiler operate efficiently and safely, and help you become a leader in the industry.

Pressure Gauge

Common faults of pressure gauges include the pointer not moving, the pointer does not return to the zero position, the pointer shakes, the surface is blurred, or water drops appear.

1. The Pointer not to Move Causes and Solutions

The pointer not to move causes

①Forgot to open the cock or the position is incorrect

②The passage of the water trap of the cock and the pressure gauge is blocked

③The pointer and the central axis are loose or the pointer is stuck

④Leakage in the weld between the spring elbow and the meter seat

⑤The sector gear and pinion are loose or disconnected

The pointer not to move solution

①Unscrew the cock or adjust to the correct position

②Clean the pressure gauge, purge the channel, and replace the cock or pressure gauge if necessary

③ Fasten the pointer on the central axis, or eliminate the phenomenon of pointer jamming

④ Repair welding leakage

⑤ Check the sector gears and pinions to make them meshed

2. The Pointer not Returning to Zero Causes and Solutions

The pointer does not return to zero causes

①The spring elbow produces permanent deformation and loses its elasticity

②The balance spring on the center wheel loses its elasticity or falls off

③The passage of the cock and the water trap of the pressure gauge is blocked

④The pointer and the central axis are loose, or the pointer is stuck

The pointer not returning to zero solutions

①Replace the pressure gauge

②Replace the hairspring or reinstall

③Clean the pressure gauge, purge the channel, and replace the cock or pressure gauge if necessary

④ Fasten the pointer on the central axis, or eliminate the phenomenon of pointer jamming

3.Pointer Jitter Causes and Solutions

Pointer jitter causes 

①The hairspring is damaged

②The movement of the connecting bolt between the free end of the spring elbow and the connecting rod, or the connecting bolt between the side rod and the sector gear is affected, and the sector gear shakes when the elbow expands and moves.

③The two ends of the central shaft are bent and partially blocked when rotating

④The passage of the cock or trap is partially blocked

⑤There is dirt or rust in the transmission mechanism such as pinion gear, sector gear or shaft

⑥Affected by surrounding vibration

Pointer jitter solutions

①Overhaul the hairspring

②Overhaul the combined bolts

③Replace the pressure gauge

④Purge channel

⑤Clean the pressure gauge

⑥ Eliminate vibration factors

4.Blurred Surfaces or Water Droplets Causes and Solutions

Blurred surfaces or water droplets causes

①There is no rubber gasket at the junction of the glass surface and the body, or the gasket is damaged, which makes the junction surface not well sealed

②There is leakage in the weld between the spring elbow and the meter seat

Blurred surfaces or water droplets solutions

①Add or replace rubber gasket

② Repair welding leakage

Water Level Gauge

Common faults of the water level gauge include leaking cock, stagnant water level, water level in the glass plate (tube) higher than the actual water level, and glass tube burst.

1. Cock Leakage Causes and Solutions 

cock leakage causes

①The material or processing of the cock is defective

②The contact surface between the plug core and the plug seat is worn and corroded

③The packing is insufficient or deteriorated, and the packing pressure is uneven

cock leakage solutions

①Replace the cock

②Grinding or replacing the cock

③Add or replace the packing, tighten the packing gland

2.Stagnant Water Level Causes and Solutions

The stagnant water level causes

①The water connecting pipe or water cock is blocked by scale, filler, etc.

②The water cock was closed by mistake

The stagnant water level Solutions

①Flush the water connecting pipe and the water cock, or use a thin iron wire to dredge

②Unscrew the water cock

3.The water level in the glass plate (tube) is higher than the actual water level causes and solutions

The water level in the glass plate (tube) is higher than the actual water level causes

①The steam cock is blocked by the packing

②The steam cock was closed by mistake

③Boiler water foams due to high alkalinity

The water level in the glass plate (tube) higher than the actual water level solutions

①Flush the steam cock or reform the packing

②Unscrew the steam cock

③Strengthen sewage discharge

4. Glass Tube Burst Causes and Solutions

Glass tube burst causes 

①The quality of the glass is not good, or there are cracks at the end of the pipe

②The center line of the upper and lower pipe seats of the water level gauge is skewed

③There is no preheating after replacing the new glass tube

④Suddenly splashed with cold water on the heated glass tube, or contaminated by oil

⑤There is no expansion gap or the packing is too tight during installation

Glass tube burst solutions

①Replace the glass tube

②Align the center lines of the upper and lower pipe seats in a straight line

③Operate according to regulations

④Prevent sudden cooling of the glass tube and remove oil stains

⑤ Reserve the expansion gap, adjust the compression packing

Glass tube burst Precautions

①There are two water level gauges on the boiler. If one of them bursts, the other water level gauge can be used to monitor the water level and replace the damaged water level.

(1)Wear a protective mask and gloves, cover the steam and water sprayed by the water level gauge with a wet sack, and quickly close the steam and water cock.

(2)Remove broken glass and packing, install suitable glass tube and new packing.

(3)Preheat the new glass tube, that is, first turn on the steam and water cock. When moisture appears in the glass tube, open the water cock slightly to discharge the soda and water mixture, then slowly close the drain cock, and gradually open the steam and water cock to normal Location.

②If the two water level gauges are damaged at the same time, stop the furnace urgently, and then replace the glass tube of the water level gauge. But when the boiler is equipped with an automatic feed water regulator or a high and low water level alarm, the glass tube of the water level gauge can be replaced without stopping the boiler.

Safety Valve

Common faults of safety valves include air leakage, failure to open when the specified pressure value is exceeded, opening before the specified pressure value, and the valve core not returning to the seat after exhausting steam.

1. The air leak causes and solutions

The air leak causes

①There is scale, sand or dirt attached to the sealing surface of valve core and valve seat

②The valve core and valve seat are worn

③The valve stem is bent or deformed or the valve core and the valve seat supporting surface are skewed

④The spring of the spring-loaded safety valve is permanently deformed and loses its original elasticity

⑤The lever and fulcrum of the lever-type safety valve are deviated, causing uneven force on the valve core and valve seat

The air leak solutions

①Purge the safety valve, if the effect is not obvious after the purge, the safety valve should be disassembled after the furnace is shut down to remove the attachments

②Replace the valve core and valve seat, or grind after turning on a lathe

③Replace the valve stem or readjust the level

④Replace the spring

⑤ Correct the center line of the lever to ensure strict verticality

2. Not opening when the specified pressure value is exceeded causes and solutions

Not open when the specified pressure value is exceeded causes

①The valve core and valve seat are stuck or rusted

②The gap between the valve stem and the housing is too small, and the valve stem is stuck after being heated and expanded

③Improper adjustment or maintenance has caused the spring of the spring-type safety valve to shrink too tightly, the distance between the weight of the lever-type safety valve and the fulcrum is too long, and the pig iron plate of the dead-weight safety valve is too heavy

④The valve channel is blocked by obstacles such as blind plates

Not open when the specified pressure value is exceeded solutions

①Purge the safety valve, if it is serious, grind the valve core and valve seat after stopping the furnace

②Appropriately increase the gap between the valve stem and the housing

③Re-adjust the safety valve

④Remove obstacles

3. Opening before the specified pressure value causes and solutions

Opening before the specified pressure value causes

①Improper adjustment or maintenance makes the spring pressure of the spring-type safety valve insufficient, the distance between the weight of the lever-type safety valve and the fulcrum is too short, and the weight of the cast iron plate of the dead-weight safety valve is not enough

②The spring is permanently deformed and the elasticity is weakened

Opening before the specified pressure value solutions

Replace the spring

4.The valve core not returning to the seat after exhausting steam causes and solutions

The valve core not returning to the seat after exhausting steam causes

①The spring is bent

②The valve stem and valve core are not installed in the right position or are stuck

The valve core not returning to the seat after exhausting steam solutions

①Replace the spring

②Reinstall the safety valve

High and Low Water Level Alarm

There are two types of high and low water level alarms commonly used in boilers: float type and electrode type.

1.The high and low water level limit water levels that do not send out alarm signals causes and solution

The high and low water level limit water level does not send out an alarm signal causes

①The power is not connected, the power fuse is blown, the electrical part is faulty or the line is faulty

②Floating ball type connecting pipe is blocked, fouling in the shell and up and down of the floating ball hinders the movement of the floating ball, and the floating ball is damaged by leaking and sinking.

③The connecting pipe of the electrode type is blocked, and the electrode is fouled

The high and low water level limit water level does not send out an alarm signal solutions

①First check the power supply, wiring and electrical parts for faults

②Recheck and clean the water and connecting pipes in the shell to remove the scale on the electrodes

③Strengthen water quality supervision, and carry out regular sewage discharge on the shell

2. The alarm water level that does not match the actual water value of the boiler and exceeds the allowable error causes and solutions

The alarm water level does not match the actual water value of the boiler and exceeds the allowable error causes

① Floating ball type The position of the high and low limit water level switches in the adjustment box has not been adjusted well or has not been adjusted at all. If the high and low limit alarm water levels are gradually higher at the same time, it may be that the floating ball has begun to leak.

② Electrode type The electrode in the measuring cylinder is not adjusted properly

The alarm water level does not match the actual water value of the boiler and exceeds the allowable error solutions

① Floating ball type Adjust the position of the high and low limit water level switches in the tank. If it is still invalid, check if the float is damaged

② Electrode type Adjust the position of the electrode on the measuring cylinder and check the insulation between the measuring cylinder and the electrode

③Strengthen daily inspection

3. The water level does not alarm or alarms but does not match the actual water level of the boiler causes and solutions

The water level does not alarm or alarms but does not match the actual water level of the boiler causes

① Floating ball type: A certain water level switch in the adjustment box fails or the switch position is not adjusted properly, and the lifting of the float ball is partially blocked.

② Electrode type The position of an electrode in the measuring cylinder has not been adjusted well, or the electrode has scale on the electrode and the insulation is poor. Some electrical parts are damaged, and the circuit is broken

The water level does not alarm or alarms but does not match the actual water level of the boiler solutions

First check the electrical parts and wiring, check the working status of the water level alarm, and strengthen daily inspections.

4. sometimes normal alarms and sometimes no alarms causes and solutions

Sometimes normal alarm and sometimes not the alarm causes

①Floating ball type: The joints of the circuit and the electrical part are virtually connected, the wire is broken or the insulation is partially damaged, the water level switch in the adjustment box is faulty, and the movement of the float is blocked.

②Electrode type: The joints of the circuit and the electrical part are virtually connected, the wire is broken or the insulation is partially damaged, and the insulation between the electrode and the measuring cylinder is unreliable

Sometimes normal alarm and sometimes not the alarm solutions

First check the electrical parts and wiring, check the working status of the water level alarm, and strengthen daily inspections

Blowdown Device

 Common faults of blowdown equipment

1. The sewage pipe is blocked

2. Dirty discharge of boiler internals

3. The installation position of the blowdown valve is not easy to operate

4. For boilers with evaporation capacity ≥1t/h or working pressure ≥0.7MPa, each drain pipe has only one drain valve

5. Leakage of the drain valve

6. The drain valve cannot be screwed

7. Cracks in the blowdown valve body

Analysis the failure of the blowdown device causes

1. Improper design, too thin drain pipe, improper installation of drain valve position

2. The leakage of the blowdown valve is due to the inconsistent operation sequence, which causes the two blowdown valves in series to wear at the same time. When a valve with a non-straight passage is used as a drain valve, the valve core is stuck by dirt, which will also cause drain leakage.

3. If the sewage is not discharged for a long time, the valve stem will be rusted and cannot be discharged

4. Poor quality of the blowdown valve, made of gray cast iron, can not withstand the impact of the blowdown, causing the valve body to crack

5. After the water pressure test, the accumulated water is not exhausted, or the boiler is stopped and the valve is frozen in winter, which is the cause of the valve body bursting and cracking

Blowdown device solutions

1. Appropriately increase the diameter of the sewage pipe, the sewage pipe and the sewage valve on the header DN≥20mm, the boiler shell boiler sewage pipe and the sewage valve N≥40mam

2. The position of the sewage pipe should be at the lowest point of the drum or header, and a sewage suction supervisor should be installed in the drum to enhance the effect of sewage discharge

3. When arranging the blowdown valve, the convenience of operation should be considered, and the operating sequence of the blowdown valve should be unified according to the operating regulations.

4. Do a good job of water treatment, sewage pipes and other related pipes should be kept clean and dry

5. The blowdown valve of the general cast iron valve body should be replaced, and the general shut-off valve and spherical valve are not suitable for the blowdown valve. Shut down the boiler in winter, and drain the stagnant water

Conclusion

Through the above content, you can have a comprehensive understanding of boiler safety accessories and valve failures, understand boiler failures and take corresponding measures to actively prevent them, and your boiler can be used more safely and lastingly.

EPCB, your private boiler system expert!

Further Reading:

Boiler Safety Series | Boiler Tube Burst Causes and Preventive Measures in Boiler Accidents

Boiler Safety Guide | Industrial Boilers'Common Accidents and Solutions

Boiler Safety Series | Boiler Water Level Accidents Causes and Preventive Measures