Maintenance of M&C SP2006-H/DIL Sampling Probe

M&C SP2006-H/DIL Dilution Probe Complete Maintenance and Troubleshooting Guide

In the field of process gas analysis, continuous sampling of high temperature, high humidity, dusty, and corrosive gases has always been a technical challenge. The SP2006-H/DIL series dilution probes launched by M&C TechGroup are based on the mature SP2000-H platform and adopt a dilution principle combining critical orifice plates and injectors, effectively solving the problems of traditional sampling probes being prone to clogging and frequent maintenance. This article is aimed at on-site maintenance engineers and system integrators, comprehensively analyzing the structural principles, installation points, startup process, daily maintenance, and typical troubleshooting of SP2006-H/DIL and SP2006-H280/DIL dilution probes, helping you quickly locate problems and restore normal equipment operation in actual working conditions.

Product Overview and Application Scenarios

SP2006-H/DIL is an electrically heated gas sampling dilution probe with a maximum heating temperature of 180 ° C (SP2006-H280/DIL can reach 280 ° C). The core design goal is to dilute the sample gas with clean diluent gas (such as nitrogen or instrument air) in a fixed ratio without changing the measurement components, thereby reducing the dew point of the sample gas, avoiding condensation corrosion, and reducing the maintenance of downstream analyzers.

Typical applications include:

Continuous monitoring of toxic gases (such as HCl, NH3, HF)

Measurement of moisture in flue gas emissions

Sampling of process gases containing high concentrations of dust or viscous particles

Sensitive processes requiring extremely low sampling flow rates (as low as 1.4 Nl/h)

This probe adopts a modular design and can be equipped with various accessories such as pre filters, blowback function, bypass injectors, heating ball valves, and pressure storage tanks according to on-site needs, adapting to process conditions ranging from atmospheric pressure to 2 bar absolute pressure.

Working principle: Critical orifice plate+injector dilution

Understanding the core technology of SP2006-H/DIL is the foundation of troubleshooting. The dilution unit is based on the principle of ultrasonic critical flow: when the pressure difference on both sides of the critical orifice plate is ≥ 500 mbar (i.e. outlet absolute pressure ≤ 520 mbar), the gas flow rate through the orifice plate depends only on the upstream pressure and is independent of downstream pressure fluctuations. This feature ensures a constant dilution ratio.

The specific process is as follows:

After being regulated by a precision pressure reducing valve, a portion of the diluted gas (such as N ₂) enters the injector and generates a high-speed jet at the injector nozzle, forming negative pressure.

This negative pressure acts on the outlet end of the critical orifice plate, maintaining the pressure difference between the front and rear of the orifice plate above the critical pressure difference.

The sample gas is drawn into the critical orifice plate through the process pipeline, probe tube, and filter element, and mixed with the dilution gas in a fixed proportion.

The mixed diluted sample gas is sent from the probe outlet to the downstream analyzer.

The dilution ratio is determined by the pore size of the critical orifice plate. The dilution ratios and sample gas flow rates corresponding to standard orifice plate types a~g are as follows (injector type I, dilution gas flow rate 480-600 Nl/h):

Orifice plate model a b c d e (standard) f g

Dilution ratio 500:1 200:1 100:1 50:1 30:1 20:1 10:1

Sample gas flow rate (Nl/h) 1.4 2.7 5.5 11 19 28 55

If using injector type II, the dilution ratio can be extended to 2000:1. Users can also adjust the dilution ratio within a certain range by fine-tuning the dilution gas pressure (-5%~+30%).

Key engineering points:

The vacuum degree at the outlet of the injector must be greater than 0.6 bar (absolute pressure<0.4 bar), otherwise the critical condition is not met and the dilution ratio will fluctuate.

Common reasons for insufficient vacuum degree include low dilution gas pressure, clogged injectors, excessively long or narrow sampling outlet pipelines.

Manual recommendation: The maximum length of the outlet sampling tube for injector type I is 50 meters for 1/4 inch and 150 meters for 3/8 inch; the diameter of injector type II needs to be correspondingly increased due to its high flow rate.

Quick search and interpretation of technical parameters

From the perspective of on-site maintenance, the following parameters are the most noteworthy:

Parameter SP2006-H/DIL SP2006-H280/DIL

Maximum heating temperature 180 ° C 280 ° C

Diluted gas inlet pressure 4.5~16 bar g (approximately 3 bar after pressure reduction) is the same as the left

The vacuum degree requirement for the sample gas outlet is>0.6 bar (absolute pressure<0.4 bar), same as the left

Process pressure range 0.9~2 bar abs same as left

Liquid receiving material SS316Ti, quartz glass FKM、 Graphite on the left

Weight approximately 30 kg on the left

Heating power 800 W (230V or 115V optional) same as left

Interpretation:

The heating function can prevent the sample gas from falling below the acid dew point inside the probe, avoiding corrosive condensate from damaging the filter element or orifice plate. If the dew point of the process gas is higher than 180 ° C, the 280 ° C version must be selected.

The inlet pressure of the dilution gas is relatively high (at least 4.5 bar) because the required flow rate and pressure difference of the injector still need to be ensured after passing through the internal pressure reducing valve.

The process pressure cannot be lower than 0.9 bar abs (i.e. micro negative pressure), otherwise the injector may not be able to form sufficient vacuum. If the process is at normal pressure or slightly positive pressure (such as flue gas), it is fully applicable.

Installation and Connection: Step by Step

4.1 Installation position and direction

Sampling points should be selected at locations where the airflow is uniform and can represent the average composition of the process, avoiding proximity to bends, baffles, or blind spots.

The probe is recommended to be installed horizontally and tilted about 10 ° towards the process direction to facilitate the reflux of condensate to the process pipeline and reduce corrosion.

It is recommended to install the diluted sample gas outlet of the probe facing downwards (not functionally necessary, but convenient for pipeline drainage).

Adequate space should be reserved around to facilitate the disassembly and maintenance of the filter chamber cover (at least 500 mm of front space).

4.2 Flanges and Insertion Tubes

The standard installation flange is 3 "150 lbs, and a 4" flange or adapter is available as an option.

The pre filter or sampling tube is screwed into the probe flange through a G 3/4 "internal thread. Commonly used ceramic filters (2 μ m, 150 mm long) or fiberglass filters (0.1 μ m).

4.3 Gas path connection

All air circuit joints are located inside the FRP (fiberglass) casing at the bottom of the probe, and are introduced into the pipeline through the CES cable entry port (suitable for outer diameters of 36-70 mm). The casing must be opened before connection, and then closed after completion.

Remarks on the size of pipeline functional joints

Test gas (calibration gas) inlet 1/4 "pipe joint with one-way valve, opening pressure 0.7 bar

The 1/4 "pipe joint at the dilution gas inlet needs to be connected to a precision pressure reducing valve and pressure gauge

Low pressure vacuum gauge interface 1/4 "pipe joint is used to monitor the vacuum degree of the injector

The 3/8 "pipe joint at the outlet of the diluted sample gas (to the analyzer) must use corrosion-resistant, low adsorption heating or tracing tubes

Bypass air inlet (optional) 1/4 "pipe joint is only used when configuring bypass injector/B or/BR

Bypass gas outlet (optional) 1/4 "pipe joint can be emptied or returned to the process

Undiluted sample gas outlet (optional) 1/4 "pipe joint for parallel measurement of undiluted sample gas

Backblowing inlet 3/8 "pipe joint for pulse blowback cleaning filter

Key precautions:

When all hoses are connected to stainless steel fittings, a support sleeve (sheath) must be used to prevent the hoses from being cut or leaking.

Dilution gas, bypass gas, and blowback gas must be clean, dry, and oil-free. Recommend using 99.999% nitrogen or instrument air.

If the moisture content of the sample gas is high, the outlet pipeline of the diluted sample gas must be traced to>dew point temperature, otherwise condensation may occur, leading to measurement deviation.

4.4 Electrical Connections

Heating and temperature control are achieved through an electronic controller (model 70304G) installed on the side of the probe. Wiring requirements:

Power supply: 230V or 115V (according to the model label), minimum wire diameter of 3 × 1.5 mm ², must be connected to an external main switch and overcurrent protection (fuse).

Low temperature alarm contact (terminals 11-12): The contact will activate when the probe temperature is below the set value of 30 ° C. It is strongly recommended to connect this alarm signal in series to the power supply circuit of the dilution gas and bypass gas solenoid valves. Once there is a low temperature fault, the dilution gas source will be automatically cut off to prevent unheated sample gas from condensing and corroding key components inside the probe.

PT100 or NiCr Ni thermocouple is used as a temperature sensor located inside the heating block.

The cable entry port must use high-temperature resistant cables (such as silicone rubber insulation) and be properly sealed.

Initial startup steps

The initial operation on site must strictly follow the following sequence, otherwise it may damage the probe or affect the analysis data.

5.1 Power on preheating

Confirm that the power supply voltage is consistent with the model label.

Close the external power switch and observe the temperature controller (70304G) display. The set temperature value has been pre-set at the factory (usually 180 ° C or 280 ° C) and can be adjusted according to the process.

Heating time is about 2 hours. When the probe temperature reaches the "set value -30 ° C", the low temperature alarm is released before proceeding to the next step.

5.2 Supply of Dilution Gas

Open the main valve of the dilution gas source and adjust the precision pressure reducing valve to the pressure specified in the injector data sheet (for example, at a typical value of 3.0 bar, the corresponding dilution gas flow rate is about 490 Nl/h and vacuum degree is -0.8 bar).

Observe the low-pressure vacuum gauge: the pointer should point below -0.6 bar (e.g. -0.7 to -0.8 bar). If the vacuum degree is insufficient (e.g. -0.5 bar), the critical orifice plate cannot function properly and the dilution ratio will change. At this point, the dilution gas pressure should be gradually increased until the vacuum degree meets the standard.

If the vacuum degree still cannot reach -0.6 bar, possible reasons may include clogged injectors, excessive resistance in the sampling outlet pipeline (too long or too thin), insufficient dilution gas pressure, incorrect or missing orifice plate installation.

5.3 Connection process

If a manual ball valve (option VA) is installed at the front end of the probe, confirm that the ball valve is in the closed state. After the dilution gas injector has stabilized, slowly open the ball valve to allow the process gas to enter the probe. Observe whether the vacuum gauge reading is stable and should not show significant fluctuations.

5.4 Calibration and dilution ratio verification

Introduce a standard gas of known concentration (such as 100% O ₂ or 100% N ₂) into the test gas interface, and the pressure of the standard gas should be greater than 0.7 bar (overcoming the opening pressure of the one-way valve).

The standard gas flow rate should be at least 3 times the flow rate through the critical orifice plate (without bypass) to ensure complete replacement of the sample gas channel.

After the downstream analyzer reading stabilizes, calculate the actual dilution ratio based on the measured value and the theoretical diluted concentration. If there is a deviation, the dilution gas pressure can be adjusted slightly (within the allowable range of -5% to+30%) for correction.

Record the dilution gas pressure and vacuum degree at this time as a reference for future operation.

Daily maintenance and typical troubleshooting

The design of SP2006-H/DIL reduces maintenance frequency, but still requires the development of periodic inspection plans based on process conditions. The following are the most commonly encountered fault phenomena and solutions.

6.1 Filter blockage

Phenomenon: The vacuum gauge reading gradually increases (e.g. from -0.8 bar to -0.5 bar), and the downstream analyzer response slows down or the concentration decreases.

Reason: Particulate matter and viscous substances in the process gas accumulate on the surface of ceramic or glass fiber filters, increasing the suction resistance.

resolvent:

Close the front ball valve (if any) and cut off the sample gas.

Remove the filter chamber cover according to section 13.4 of the manual (use the handle to rotate and loosen the clamp, and pull out the cover).

Check if the compression screw of the filter is loose, and remove the filter element.

If there is visible dust accumulation on the surface of the filter element, compressed air can be used to blow it from the inside out; If it is severely blocked or broken, replace the spare filter element directly (recommended spare parts 90S0020 ceramic 2 μ m or 90F0125 glass fiber 0.1 μ m).

Simultaneously check the sealing ring of the filter element (93S0045, Viton) ®） Replace the O-ring (93S0020) inside the cavity cover if it is deformed or hardened.

After installation, re-establish the dilution gas and observe whether the vacuum degree is restored.

Preventive suggestion: If the concentration of process dust is high, a reverse blowing function (option/BB or/BB/F) can be selected. Regularly (such as every 4 hours), 6 bar compressed air can be introduced to blow the filter in reverse, which can greatly extend the life of the filter element.

6.2 Critical orifice plate or injector blockage

Phenomenon: The dilution gas pressure is normal or even high, but the vacuum degree is very low (such as -0.2 bar), and the dilution ratio is significantly abnormal (calibration failure of standard gas).

Reason: Ammonium salts, tar, polymers and other substances in the sample gas deposit on the micropores of the orifice plate (with a diameter of only a few tens of micrometers) or the nozzle of the injector after cooling.

resolvent:

Turn off the heating, cut off the dilution gas, and wait for the probe to cool down to room temperature.

Open the FRP shell, loosen the thermal clamp and clamp, and remove the dilution block (see Figure 16).

Carefully remove the critical orifice plate and/or injector using specialized tools (randomly provided). It is strictly prohibited to use metal needles or other hard objects for mechanical dredging, as it may damage the precision hole opening.

Place the orifice plate and injector into the ultrasonic cleaner and clean with a mild cleaning agent (such as deionized water or acetone, depending on the nature of the sediment) for 10-15 minutes.

After removal, dry it with clean compressed air, check the O-ring (93S0020 or 93S0025), and replace it if it is damaged.

Reinstall the dilution block to ensure that the O-ring is in the correct position and tightly pressed in place. Attention: The orifice plate has directionality, and the side with a conical surface or mark should face the intake direction.

Reinstall the dilution block, restore heating and gas supply, and test the vacuum degree.

Experience tip: If there may be easily crystallizable substances (such as NH ₄ Cl) in the process, it is recommended to increase the heating temperature of the probe to above 200 ° C, or choose the 280 ° C version, and keep the dilution gas continuously flowing (without interruption during shutdown) to prevent reflux crystallization.

6.3 Frequent triggering of low temperature alarm

Phenomenon: The temperature controller displays large temperature fluctuations or cannot reach the set value, and the low temperature alarm relay acts.

Possible reasons:

The heating element is damaged (open circuit). Measure the resistance of the heating rod with a multimeter. The resistance of the 230V/800W model is about 66 Ω, and the resistance of the 115V/800W model is about 16.5 Ω. If infinite, replace (spare parts 93S0015 or 93S0017).

PT100 or thermocouple malfunction. Measure the resistance or millivolt signal of the sensor and compare it with the standard calibration table.

Poor thermal conductivity: Thermal grease (93S0018) is not applied between the heating rod and the heating block, or the thermal clamp is not tightly pressed.

Excessive wind speed in the environment leads to rapid heat dissipation, and a windproof cover needs to be installed.

6.4 Low readings during calibration of standard gas

Phenomenon: When a known concentration standard gas is introduced, the downstream analyzer displays a value lower than the theoretical calculated value.

Possible reasons:

Insufficient flow rate of standard gas, incomplete replacement of dilution gas. It should be ensured that the standard gas flow rate is ≥ 3 times the gas flow rate of the orifice plate sample.

There is a leak in the calibration gas circuit, which dilutes the standard gas. Check all joints with a leak detector.

Dilution is greater than actual (i.e. excessive dilution). Check if the dilution gas pressure is too high or if the orifice plate is worn.

The linear deviation of the analyzer itself should be calibrated separately with zero gas and range gas first.

6.5 Backblowing function failure (if configured)

Phenomenon: After starting the blowback, there is no instantaneous increase in filter pressure or poor blowing effect.

Reason:

The pressure of the blowback air source is insufficient (at least 6 bar is required).

The blowback valve (pneumatic or electromagnetic) is not activated. Check the control signal and valve body.

The accumulator tank (if optional) is not pressurized or leaking.

The opening pressure of the check valve (/BB) is 0.7 bar. If the blowback pressure is lower than this value, it cannot be opened.

Suggestions for spare parts selection

Based on on-site maintenance experience, it is recommended to keep the following vulnerable parts on hand (refer to Section 18 of the manual):

Spare part number description, replacement cycle suggestion

90S0020 ceramic filter cartridge 2 μ m 150 mm 3-6 months (depending on dust)

93S0020 O-ring (for dilution block, chamber cover) annually or after disassembly and assembly

93S0045 filter gasket (Viton) ®） Every time the filter element is replaced

When the 93S0015/17 heating rod (230V/115V) malfunctions

When the temperature sensor of 93S0059 PT100 malfunctions

When the 93S4406 dilution block (without orifice plate) is severely corroded

93S4420 complete dilution unit (including specified orifice plate), specify dilution ratio when ordering as needed

Precautions for shutdown and storage

When the system needs to be shut down for a long time or the probe needs to be disassembled:

Close the front-end ball valve and cut off the process gas source.

Keep the dilution gas flowing for more than 30 minutes and blow off the residual sample gas inside the probe.

Turn off the heating power and wait for the probe to cool down to ambient temperature.

Cut off all gas sources such as dilution gas, blowback gas, and standard gas.

If the probe is removed from the flange, the inlet and outlet of the sample gas must be sealed with a protective cover to prevent moisture from entering the corroded interior.

The probe should be stored in a dry, frost free, vibration free room, away from direct sunlight.