Check valves malfunctioning

Today s HPLC pumps have sophisticated designs honed by decades of incremental improvements. They are also more reliable and easier to maintain than their predecessors. Short seal life and check valve malfunctioning seen in the early models are no longer problems. In this section, the principle of pump operation is described with an emphasis on advances leading to higher reliability and performance. A discussion of system dwell volume is included. 

The compatibility of an organic solvent with a buffer in the mobile phase must be checked as the buffer salts can be easily precipitated when using on-line mixing, thus causing frit blockage, check valve malfunction, and other problems. 

This device is useful for compensating for possible variations of the motor speed due, for example, to power problems. However, it cannot correct the flow--rate variations due to fluid compressibility and system compliance, to check valve malfunction or to correct any leakage in the hydraulic circuit or mobile phase circuit. 

PCV - 34 Malfunction Flow releasee to flare, including recycle froai compressors 1natall check valve downstreaai of ESV to prevent back flow of gas froai the compressors tilth block valve and one-inch bypass for starting end purging NOTE Check valve and one inch bypass Installed refer to revised PtIO Rev. 0 Recycle on compressor will open - system will not shut down... 

Figure 10.3. (a)Pressure profile of a normal HPLC pump showing pressure fluctuation <2%. (b) Pressure profile showing significant fluctuations of a malfunctioning pump due to a bad check valve or a trapped bubble in the pump head. Figure courtesy of Academy Savant. 

Pressure too low Lower than expected system pressure is caused by leaks (piston seal, column connections, injector), pump malfunctions (lost prime, air bubbles in pump head, vapor lock, faulty check valves,broken piston), or inadequate solvent supply (empty solvent reservoir, plugged solvent sinker, bent solvent lines, or wrong solvent mixture). Problem diagnostics can be made by visual inspection for leaks and by monitoring the pressure reading of the pump. 

Can feed, auxiliary, intermediate and final products enter pipes or parts of the plant where they should not be, due to operator mistakes or malfunctions (e.g. cooling water or products in drinking water pipes, oxygen or air in inert gas pipes etc.) What safety measures are implemented to prevent this (e.g. check, valves, double shut-off valves with a vent, interlocks of valves etc.) ... 

Open the cylinder valve slowly until the tank gauge on the regulator registers the cylinder pressure. At this point, the cylinder pressure should be checked to see if it is at the expected value. If there is a large variance, check for leaks, cylinder valve malfunction, or pressure gauge malfunction. 

Weeping safety valves not only cause undesirable watermarks and steam losses but may indicate valve malfunction. A check for excessive amounts of system makeup water should be made by means of a water meter on the inlet line. 

Malfunctioning of safety related check valves could create unacceptable situations during accidents and contributes to the risk associated with postulated core-melt accident sequences. 

Sin eunnary failure aiae up to 25 aquare inchea in the outlet downcomer upetream of the check valve can be accommodated with a clean aeparation with the aaaumptiona made which Include complete malfunction of the dump ayetern. 

What about Preventive maintenance A preventive maintenance program should be established in consultation with those responsible for the upkeep of the chamber during normal use. This should be done after successful qualification and prior to releasing the chamber for use. Components that are prone to malfunction due to normal wear and tear include solenoid valves, humidifier floats, and recirculation-fan drive motors. These components should be checked or replaced on a regular basis to prevent or minimize chamber downtime. 

Improperly prepared mobile phase contaminated mobile phase. —> Prepare fresh mobile phase. Check pump-proportioning valve for malfunction. 

Organizational elements must be checked and justified carefiiUy as to required time and feasibility. It must be ensured that they can be performed easily and quickly enough after the occurrence of a malfunction. The organizational elements must be laid down in operating instructions and regularly trained by the personnel (cf. Chap. 5 and Sect. 9.7). Furthermore certain technical equipment must be provided to support manual interventions, e.g. a hand-operated shut-off valve. 

For LC resins having very low viscosity, the check ring valve should be ensured for proper functioning. Due to malfunctioning of check rings, inconsistent parts, short shots and poorly formed weld lines are observed. 

---