Check valves replacing

Leaks in pump check valve or seals. Replace or clean check valves replace pump seals. 

In order to properly preserve this well-maintained facility, it was desired to replace the defective 300 psi R.F. check valve on Pump B quickly, as part of the seal replacement job. Maintenance personnel had searched for a 12 in. check valve but had found only one similar valve. Unfortunately, there was not an exact ANSI check valve replacement immediately available. 

LC pumps—replace or clean piston seals, pistons, in-line filter, solvent filter sinkers and check valves. 

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. 

Spare parts that are needed are compression fittings and ferrules, plunger and injector rotor seals, an extra plunger and seals, column filters, and injector needle port seals. If you do not use pacification, you might want to keep a set of check valves on hand. I always have one coil each of 0.01- and 0.02-in tubing in addition to my column blank. A replacement solvent inlet line with a porous stone is useful in case of corrosion. If you filter solvents, you need cellulose, nylon, and Teflon filters. You also need a back-up lamp for your detector. 

Pacification is a technique for removing organics and buffers from HPLC metal and Teflon surfaces and protecting them from salt corrosion with 6 N nitric acid (see Chapter 4). First, remove the HPLC column and replace it with a column bridge. Do not flush this wash into the mass spectrometer. Wash the system with water. Remove the column and replace it with a column blank. Flush with 6 N nitric acid for at least 30min, then overnight with water. Ensure the effluent pH is back to that of lab water. Replace the column and flush with mobile phase. This should be done at least once a month to clean check valves, line, and injectors. Under no circumstances should this wash be done with an HPLC column in place or into the mass spectrometer ... 

Periodic-pump pulses Service or replace pulse damper purge air from pump clean or replace check valves. 

Proportioning valve failure —> Check diaphragms, replace if leaky check for fitting damage, replace. 

Filtering mobile phase prevents often replacing inlet frits and check valves. Degassing mobile phase prevents bubble formation. 

Other connectors to the tank could be used after installing the check valve in the tank. For instance, a DESO stem and body, and/or other type of quick disconnect will hold the pressure in the line and in the tank. These other connections make it possible to disengage the tank from the system to remove it and/or replace it with another tank. 

Blocked or leaky check valves can probably be fixed by sonicating them. Perhaps a number of solvents need to be tried, e.g. water with detergent, tetrahydrofuran or dichloromethane. Some valves fall apart when they are removed from the pump head (beware of loss of the ball ), some can be opened and some are a unit which should not be opened. With the first two designs the ball can be replaced, maybe also the seat, when these parts are scratched and do not seal well any longer. The other types of check valves must be replaced totally if they do not work properly and if a treatment with ultrasonics does not help. 

Figure 7 Schematic diagram of semipreperative-scale SFC chromatograph 1 carbon dioxide supply 1 a regulator 2 prechiller/heat exchanger 3 SD-1 Varian pump with (7) 200-mLpump head with special check valves 4 modifier reservoir 5 SD-1 modifier pump with (6) 200-mL standard pump heads 8 check valve 9 inlet pressure transducer 10 injection valve 11 check valve to prevent blow-back 12 mixer 13 fluid temperature preconditioner 14 column 15 column oven 16 uv detector 17 outlet pressure transducer 18 back-pressure regulator 1 9 evaporator 20 restrictor 21 trim heater 22 selection valve 23 peak detector 24 bank of collection vessels (or cassette) 25 individual collection tubes/bottles 26 pressure relief valves 27 waste container, waste vent. The manual cassette can be replaced with an automated cassette fed by a robot holding 128, 25 x 150-mm or 338, 16 x 150-mm test tubes, or with 7 large bottles.

Common maintenance tasks that can be easily performed by the user are the replacement of solvent filters (sinkers), in-line filters, check valves, and piston seals. Most modern HPLC pumps are designed for easy maintenance, with front panel access to many internal components. Figure 10.1 is a diagram of a slide-out pump unit showing the two pump heads with check valves, the purge valve, the in-line filter, and other components. Procedures for replacing some consumable items are summarized below ... 

Performing the obvious or easy things first (i.e., replace check valve if pump pulsation is higher than expected). 

Check valve Contamination from mobile phase Contamination from pump seal Buffer salt deposits cause blockage Years—with correct care Replace pump seals Flush with HPLC grade solvent Use filters... 

The value of root cause analysis is that conclusions are reached that may address a much broader range of issues than those immediately to do with the event being investigated. For example, the initial evaluation of the reverse flow problem in the standard example finds that the check valve failed. Further examination identifies a root cause that all check valves purchased from the manufacturer of that particular valve are unreliable and need to be replaced. This conclusion may, in turn, suggest weaknesses to do with the company s overall procurement system. 

The team should be careful about making recommendations that are too specific. For example, a recommendation to do with the standard example could be Replace all check valves from vendor A with check valves from vendor B. However, the mechanical engineer at the facility may have additional information to do with check valves in this service such that the recommendation will not achieve the desired effect. It is better in such circumstances to generate a finding such as The integrity of the check valves was determined to be unacceptable, and a new mechanical integrity policy regarding these check valves is required. ... 

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