Article link: https://instrumentationtools.com/differential-pressure-transmitter-working-principle/
Question:
Q. Local gauge glass normal but remote level gauge showing high level, cause?
Possible Reasons:
- Leaky bypass valve (pressure regulating valve)
- Defective primary element (primary sensing element-diaphragm)
- Defective transducer
Q. How to blow down DP cell sensing lines?
- Close low pressure sensing line valve.
- Close high pressure sensing line.
- Open bypass valve connecting L.P and H.P side.
- System ready for blowdown.
- Open low pressure side blowdown valve, wait for about 10 seconds, then close it.
- Open H.P side blowdown valve, wait for about 10 seconds, then close it.
Q. Boiler tube plugging:
.btp .boiler tube pluging
Procedure:
- Identify the defective tube when the boiler is pressurized, burner cut out.
- Take permission from office.
- Shut down boiler according to instruction manual, let it cool down, ventilate before entering.
- Whole process may take 2/3 days depending on the severity of tube failure. Take preparation accordingly.
- Prepare enclosed space entry permit, read, and understood by working personnel, have It signed by master.
- Boiler is provided properly sized tube blanks, use them to blank off the tubes.
- Tube needs to be blanked off on both end, clean tube ends.
- Insert tube blanks by hammer, weld if necessary.
- Fill up boiler with feed water and check for leakages under pressure.
- Fire up boiler slowly according to instruction manual.
Control:
Boiler Auto combustion Control:
.acc .bacc
MV= manipulated value (set point, process value difference)
PV=process value (measured value)
A/H=auto or hand
Description:
Initially, MV=SV, PV1=C.SP1, PV2=CSP2, a ≈ b, c ≈ d.
If steam demand ↑, MV↓
O/P of R/A Master Controller ↑, c↑ , a↑
c > d, d passes through LSS,
so no change in CSP1,
But a > b, ‘a’ passes through HSS,
CSP2↑, PV2↓ wrt CSP2
O/P of D/A Air flow controller ↓
ATC air damper opens more,
Combustion Air flow ↑, d↑,
d passes through LSS since d < c,
CSP1 ↑, PV1↓ wrt CSP1,
O/P of R/A Oil flow Controller ↑,
ATO oil control valve opens more,
Steam pressure restored to SV within a few cycles due to I-action of the Master controller. The control scheme above ensures that air is increased ahead of fuel to prevent fuel-rich condition when load ↑. And similarly, fuel will be decreased ahead of air to prevent fuel-rich condition when load ↓