purging hplc pump. b. purging hplc pump

 
bpurging hplc pump  Press the EDIT/ ENTER key

8. Program the pump to purge the column with strong solvents. This will redirect the solvent flow to the waste exit of the valve instead of passing through the whole system. solvents. Vanquish Binary Pump C: Up to 700 bar (10,000 psi) and 10 mL/min. From my little experience i learnt that it may be due to air trapped in. (Prime each pump head separately. The 1260 Infinity II Flexible Pump is a quaternary UHPLC pump that provides gradient formation and solvent blending from up to four solvents. Maintaining Your Agilent 1100 Series HPLC System Optimize performance and maximize efficiency in your lab. First, disconnect connection (1) in Figure 1 and pump the solvent (to check the backpressure tube 4)). b Select Set up pump. ), prime system if necessary. Pump 100% isopropanol through the pump for 3 minutes. If a purge valve is not functioning correctly, it can lead to the vehicle losing power or stalling unexpectedly. The pump (s) should be run (column disconnected and bypassed) run with a solution of pure HPLC grade water to try and rinse the material off. Priming and Purging the 1525 Binary HPLC Pump. TP01408 RUN STOP EDIT ENTER MENU Waters 515 HPLC Pump Draw-off valve Seal wash hole (not visible) Pump head assembly High. Basic HPLC System Components. Press “Menu” till the purge appears on the screen. Run each pump for 2 minutes. High Priced Liquid Chromatography. Enter terms to search videos. Purge Solvents a. This is a prevention step. Before the actual compression process begins (see Fig. If problem. (Most ternary pumps actually have four solvent reservoirs. Flexible Pump The Agilent 1290 Infinity II Flexible Pump improves your efficiency by combining the performance of a high-pressure mixing UHPLC pump with the flexibility of a low-pressure mixing UHPLC pump. don't forget checking the purge valves. Sonication: ultrasonic baths as a stand-alone. Fig. Purge pump at high flow rate (e. Always do this one channel at a time (e. 2. If problem persists, flush system with 100% methanol or isopropanol. Currently loaded videos. 5. HPLC Pump: The HPLC pump produces high pressure that gives a continuous and reproducible flow to the mobile phase throughout the HPLC system. On – line vacuum degassing is available on most commercial available systems. Purge valve Purge function Remove the purge valve waste line and the capillary from the purge valve outlet. *Run to run RT variation of ±0. (2) Dry Priming using the HPLC pump to draw the mobile phase out of the bottles, through the lines, degasser channels and to the pump head or multichannel valve. The Waters 1500 Series HPLC Pump Installation and Maintenance Guide has five chapters and four appendixes. Eluent may then be allowed to progress through the IC system, and the pressure monitored. Rebuilding the Reference Valve. Some bubbles may be generated from the suction filter head dipping in the mobile phase. 6. The display will show messages ‘Start PURGE’ and ‘Press ENTER to confirm’. The target url is a user manual for the Agilent 1290 Infinity Quaternary Pump G4204A, a high-performance liquid chromatography (HPLC) device that can handle a wide range of flow rates and compositions. |The 1290 Infinity II Bio Flexible Pump. Use the keypad to type in the solvent composition for pumps A, B, C, and D. Abstract and Figures. g. Overlay of 6 pump proportioning chromatograms in 10% gradient. Introduction 4 1. Mass spectrometry, chromatography, spectroscopy, software, dissolution, sample handling and vacuum technologies courses. b. Prime the HPLC pumps under the following conditions: - starting the pumps for the first time after it has been idle for more than 24 hours. 8. g. A damping unit is connected between the two piston chambers. off. 1ml/min2 g. The system must be primed to remove air bubbles and for the pump to function properly. keep the system at this flow rate for about 10 minutes to equilibrate the system without the Column. Pump Types LPG pump type Eluent composition at the low pressure side => Before the pump head Eluent is composed through proportioning valves Eluent segments pass working and equilibration cylinder Up to four solvents can be mixed HPG pump type Eluent composition at the high pressure side => Behind the pump head UltiMate 3000 Series: Pump Series Operating Instructions Page I Declaration of Conformity (Original Declaration) Product: UltiMate 3000 Series Pump Types: LPG-3400AB, LPG-3400M and LPG-3400MB For stainless steel flow paths, proceed to Step 6; For PEEK flow paths, the cleaning procedure is completed. Purge the Pump (whenever changing buffers) a. UltiMate 3000 Series: SD, RS, BM, and BX Pumps Page II Operating Instructions. Liquid Chromatography. - For Quick Start: Click the "Press to make a single injection" button in the Acquisition. Figure 6: Pump head with purge valve and outlet to autosampler. PROCEDURE: Flush the system using one of the cleaning mixtures as described in the cleaning. Before using an HPLC system, you should prime all of the lines in your HPLC pump. • Mast kit with mixer, purge valves and manual injector • Pre-formed 0. 9-0. This pump enables quaternary solvent delivery at pressures up to 800. Close the purge valve. 5 Close the purge valve, set the flow to a rate adequate to achieve a pressure of 350 bar. Replacing a Check Valve Cartridge. At the extreme, air in the pump will cause the pump to stop delivering mobile phase to the column. Purging has only helped to reduce. 1, 3, and 4. Before using an HPLC system, you should prime all of the lines in your HPLC pump. Optional solvent selection valves can be added for solvent. Set flow to 0ml/min f. HPLC pumps are designed to pump liquid, not air. PROCEDURE: Flush the system using one of the cleaning mixtures as described in the cleaning. 998. We have been experiencing some pressure problems on our hplc lately and the problem is mostly fluctuations in the pump head. By the end of this video you will learn how to safely and quickly swap that suck. High concentrations of mobile phase buffer in your system (e. You basically tell it to shut down when the pressure drops to a specified level. 3601-EN Revision 5. When you vent the system, the components are turned off and the rough pump turns off. Mobile phase is passed through porous polymer tubing placed in a vacuum chamber. Open the manual purge valve or use the purge command,. HPLC Starter Kit G4201-68707 195 HPLC Starter Kit G4202-68707 195 HPLC System Tool Kit 196 Bottle Head Assembly 197 Solvent Cabinet 198. This can be caused by reduced fuel and airflow in the system, resulting in misfires and power loss. The manual covers installation, operation,. 1 and purge the pumps for 5 min at a flow rate of 5 ml/min. After the valve sonication procedure, it is suggested to purge the pump with water at 60 degrees, keeping the purge valve open. 3. - Troubleshooting the degasser always needs to be linked with troubleshooting the mobile phase. Agilent University. A key element of its user-friendly functionality is the accessibility of the system for. Purification Sample Management From HPLC fraction collection and aspiration to sample injection, Waters provides easy-to-use sample management options. purge is complete, enter a flow of 1 mL/min and 100% B. 11 Click everything on. It is column chromatography. I am working with HPLC Shimadzu 20AD fitted with LC20AD. Loss of Power. ⬇️ Get Affordable and Dope Lab Consumables Here ⬇️(No pun intended, unless you're a cannabis lab, then pun intended)to Connect with. 2:19. Open the black purge valve on the front of the quaternary pump by turning it several times counterclockwise. If you see a major leak from the bottom of the pump head or in the gap between the two pump head, please contact your local Agilent support representative. High Pressure Liquid Chromatography. Open prime/purge valve (in the case of Chrom Tech pumps, you turn the knob counterclockwise one to two turns. 88 Service Handbook for 1050 Series of HPLC Modules - 11/2001 Pumps: General Information Specifications Specifications Table 2 Specifications of 1050 PumpsHi,when I do wet prime/dry prime in hplc ? Thank you. HPLC pumps incorporate single or dual piston, syringe, or diaphragm pump designs. ), prime system if necessary. Detector – responds to the separated analytes emerging from the HPLC. Steps to follow: Store the column in an appropriate solvent (check column information sheet) When you remove the column, add a column union so the detector gets flushed as well in the following steps. 2. 2 shows the flow line during LC-2010 analysis. Pump – Open the purge valve and purge every solvent channel with 5 mL/min for 5 minutes to remove bubbles in your solvent lines (Note: if the backpressure at purging is higher than 10 bar, please replace the PTFE frit in the purge valve) – Make sure that the flushing solvent is mixable with the storage solvent of your solvent channel. Close prime/purge valve. 17: Ready Check Results window appear s after the NC pump blocks purge is executed 2. 3. purge를 실행하기 전에 꼭 DRAIN 밸브를 열어주고 실행하며, purge가 끝난 후 밸브를 다시 닫아줍니다. It can mainly divided by two types 1. Request a Certificate. Products. you will need to • General cleaning Daily first re-prime the pump by purging the air from all the lines. From my little experience i learnt that it may be due to air trapped in. derivatization reagent, microdialysis liquid,…)The 1290 Infinity II Bio Flexible Pump is a UHPLC pump consisting of biocompatible material, designed for use in biopharma and other applications utilizing high-salt and extreme-pH conditions. Reducing the diffusion path to improve degassing. 1 Procedure for Operation of HPLC pump: • Ensure that all the cables and power cords of the pumps are connected properly. (1:27min) Exchanging the Purge Valve Frit or the Purge Valve (3. If problem still persists, contact system manufacturer. To start purging, press the "Purge" bottom on both LC-20AD and SIL-20AC. ResearchGate | Find and share researchpump for extended seal lifetime † Setting upper and lower pressure limits will turn off the pump, e. If the pressure drops off suddenly (by more than a few kgf/cm 2), the backpressure tube is clogged. A damping unit is connected between the two piston chambers. Purge Line Figure 1 322 HPLC Pump. Purge each channel for 5-10min 3. As well as excellent accuracy, it has very small delay volumes of ≤ 350 μL. If you have an Agilent 1260 Infinity Isocratic or Quaternary Pump, remove the tubing to your passive inlet valve (PIV). High Pressure Liquid Chromatography. A = 100%). Turn pump to ‘On’ 7. 22μm porosity membrane filter. Close the cover. Turn . E. Then, turn it slightly past the initial resistance (check this). Read Less. For stainless steel flow paths, proceed to Step 6; For PEEK flow paths, the cleaning procedure is completed. 결과 및 정리. Varian Modular Analytical HPLC Systems Figure 1. 9-0. Algae Growth in HPLC Systems 53 5 Optimizing Performance 55. Delivering Scientific Insights to Improve Human Health and Well-Being. High Priced Liquid Chromatography. Always do this one channel at a time (e. UltiMate 3000 Series: Pump Series Operating Instructions Page I Declaration of Conformity (Original Declaration) Product: UltiMate 3000 Series Pump Types: LPG-3400AB, LPG-3400M and LPG-3400MB DGP-3600A, DGP-3600AB,. Disconnect tubing at guard column (if present) or analytical column inlet. Once the system is purged, set the flow rate at 0. HPLC pumps are designed to pump liquid, not – Improve Peak Shape for Ionizable Compounds air. On the front panel of the pumps, press the VP button. 1 A) Calibration of Pump:-. Therefore, to estimate how much volume is required for a purge, check the volume specification of the inlet tubing, the degasser and the pump that you are using, then double it to give an approximate purge volume. Pump – Open the purge valve and purge every solvent channel with 5 mL/min for 5 minutes to remove bubbles in your solvent lines (Note: if the backpressure at purging is higher than 10 bar, please replace the PTFE frit in the purge valve) – Make sure that the flushing solvent is mixable with the storage solvent of your solvent channel. Load a Method a. Draw approximately 20 mL of fluid. Page 103 • Operation Figure 29: Dwell volume. For more information on purging the pump, see the reference. Use only HPLC-grade solvents and water filtered through 0. Peak shape C. 02-0. Residues or contaminations may block filters or capillaries. Hello Kancheri this is the purge valve for Agilent 1260 G1312-60071 | Agilent You can check in the manual at page 154 on HOW to replace purge valve with this. OBJECTIVE: To clean and flush an Alliance HPLC System or an ACQUITY UPLC system to remove contaminants. 0 ml/min flow for more than 2. 1 Turn on LC20AD (component 4) and SIL20A (component 3). Flow rate range of 0. • Press “Menu” till purge appears on screen. Label bottles correctly with bottle content, and filling date / expiry date. • After few seconds, the display will show, Flow 1. c. Figure 2 shows how to perform the purge for an i-Series. ) If system has check valve, loosen valve to allow air to escape. g. 2. 05 min is normal however the behavior of the method should be used to determine what is a normal variation. Proper storage of HPLC columns will increase longevity and performance. • Clean the bottle head assembly using lint-free wipes to minimize solvent carryover. They are available in various configurations (→ Supported Configurations, page 5) and can thus be used in numerous laboratory environments. Prime the pump with degassed solvent. Frit, PTFE, 5/pk Add to Favorites + Create New list Item successfully added to your list Subscribe to this item in cart or checkout. 3601-EN-5. For more information, please visit Connect the Restriction capillary (5022- 2159) to the purge valve. 3. 3:36. This purging is carried out for several hours or overnight, depending on the system's size and the degree of contamination. Set maximum flow gradient to 0. Therefore, the term "the Purge pump and attempt to clean check valves. If the preceding step does not solve the issue, remove the purge valve and start the pump. Purging the solvent pumps 1. This pump enables quaternary solvent delivery at pressures up to 1300 bar and flow rates up to 5 mL/min. (Prime each. if the column gets blocked or leaks occur † Automated electromagnetic purge valve for convenient system setup Agilent 1200 Series fraction collectors Designed for lowest delay volumes to minimize peak dispersion and carryover. The two channels are fed into a low-volume mixing chamber which is connected via a restriction capillary coil to a damping unit and a mixer. The target url is a user manual for the Agilent 1290 Infinity Quaternary Pump G4204A, a high-performance liquid chromatography (HPLC) device that can handle a wide range of flow rates and compositions. First statement: Don’t let it run dry. 1290 Infinity II High Speed Pump User Manual. Then wash them out with water and re-assemble them on the pump head. Select this procedure when you want to prime and purge any 1525 Binary Series Pump. Run at high flow: Next, Dolan advises to run the pump for several minutes at high flow (e. Put the Pump A in your buffer. 6:51. Use solvent inlet filters to protect the system from incoming particles. . Dear Huq, check out the whole tubing starting from Pump to the Column inlet for any air trapped, purge the pump for few minutes. The table below describes the material covered in this book. From my little experience i learnt that it may be due to air trapped in. pump program to 90/10 water/ACN to flush the column for 15 min at 1. UltiMate 3000 Series: SD, RS, BM, and BX Pumps Operating Instructions Page I Declaration of Conformity (Original Declaration of Conformity) Product: Thermo Scientific Dionex UltiMate 3000 - Pump Types: ISO-3100SD, ISO-3100BMWe have been experiencing some pressure problems on our hplc lately and the problem is mostly fluctuations in the pump head. eluent through the pump for purging. Newsroom; Company Information;HPLC Setup Section 6. The preparative LC system performs automatic simulations using the pre-preparative results. Dolan advises that this will clear. 0 • November 2022 *4820. Purge Valve Assembly: 1 - Valve body, 2 - PTFE frit with groove, 3 - Seal cap. We routinely see HPLC systems with white fluffy crystals built up around the pump heads, pistons and various fittings from lack of maintenance on a daily basis. A = 100%). • Purge each channe lwtih 25–3m. Pump head assemblies Draw in and deliver eluent. 5 kgfcm -2, for example) for 10 to 30 minutes to purge the air from the mobile phase. the user. If tiny air bubbles are observed in the lines continuously, it’s. HPLC에서의 purge는 불필요한 기체를 제거하기 위해, 2. 1 Introduction Purpose of the User Manual The User Manual provides you with instructions and information to run the ÄKTA™ avant system. Operable in constant flow or constant. 1:55. This video demonstrates the proper procedure to manually prime the pump on a Shimadzu LC 40 instrument. The 1290 Infinity II Flexible Pump combines highest performance, methods compatibility, and. Initiate solvent flow by pushing the “PUMP ON/OFF” button on the front of the pump, then press “ENTER”. DO NOT PUMP ANY FLUSHING SOLVENT THROUGH THE SEAL WASH LINE, OR INJECTION NEEDLE LINES. 2 1. c Enter the new parameters in step 8, and click OK. Vent. 2 Push the “conc” button on LC20AD. Request Information. 5301 Stevens Creek Blvd. Purge the system to remove air bubbles and make sure the solvent is the same solvent when the GPC column is placed. Open the manual purge valve or use the purge command, depending on the pump type. A purge valve including a PTFE frit is fitted at the pump outlet for convenient priming of the pump head. 1–1% solution by volume is sufficient. 06% or 0. The sensor signals the control board when the vacuum is below a preset level. 1) Locate the pump draw-off valce (handle located on front of the pump) and priming syringe. 1 Turn on LC20AD (component 4) and SIL20A (component 3). Use a syringe to draw enough solvent for completely filling the tubings to the pump inlet before continuing to prime with the pump. Algae Growth in HPLC Systems 81 Prevent Blocking of Solvent Filters 82 Normal Phase Applications 83 4 Optimizing Performance 85 Using the Degasser 86. The pump assembly includes a pump head with an active inlet valve which has an replaceable cartridge, and an outlet valve. Among the various technologies developed for chromatography,. , 5-10 mL/min. This post continues the series of Chromatography Explained and will focus on introducing HPLC and how. Flush the HPLC system with hot water (80-100°c) through all channels using a union in place of column with 5. Figure 2 shows how to perform the purge for an i-Series. Initially, the pressure was unstable. RCM in the Quat Pump module i. It provides HPLC systems with an automatic, continuous method of removing dissolved gases from mobile phases. 1. Learn essential HPLC maintenance tips. For. If problem persists, flush system with 100% methanol or isopropanol. 2HPLC is a High Performance liquid Chromatography. [][]Fill up & attach Labels of the solvent reservoirs properly. Turn . The high-precision P680 HPLC pumps are high-quality modules designed for HPLC analysis as part of a Dionex Summit HPLC system. Retention. Delivering Scientific Insights to Improve Human Health and Well-Being. † Minimizes carry over for viscous samples, minimum injection volumes, maximum sensitivity and if the Wellplate Autosampler is. RCM (right click mouse) in the Quat Pump module i. ) The easy to use and economically designed LC-40D pump enables reliable HPLC chromatography in isocratic, binary, or LPGE modes. Flush the pump with 100% filtered, distilled water for at least 3 minutes. It is column chromatography. Discover the efficient LC-40D pump for routine HPLC applications up to 44 MPa (440 bar. you will need to • General cleaning Daily first re-prime the pump by purging the air from all the lines. The manual is in English and can be downloaded as a PDF file. Chapter/Appendix Description Chapter 1, Overview of the Waters 1500 Series HPLC Pump Describes the. Draw syringe back to prime. If still you have the same problem, checkout the rest of tubing. Email Priming and Purging a 1525 Binary Series HPLC Pump to a friend ; Read More. The impact of this type of clogging will be gradual, not sudden. "Chromatography" is a technique for separation, "chromatogram" is the result of chromatography, and "chromatograph" is the instrument used to conduct chromatography. Moreover, if the faulty purge valve completely blocks the engine, it cannot start or run. Operating principle. Typically a 0. Air bubbles can create such flow anomalies. Thus, the gradient delay volume of an HPLC system is the volume that the pump must deliver until a change in solvent composition reaches the column inlet. Waters Student Academy 2023. Remove and disassemble the pump head. solvents. United States. Turn on the pump flow rate to 3 mL/min through your CDS Software, Lab Advisor or through the Instant Pilot and open. If adequate purging cannot be achieved with auto-purging or a suction tube does not contain liquid, for example, use the following procedure to manually purge with a syringe. • Vacuum chambers – Contain the gas-permeable eluent channel. The 1260 Infinity II Quaternary Pump combines proven reliability with highest flexibility in automated. Figure 1 Overview of the binary pump Purge valve Active inlet valve Mixer Outlet valve. Pump heads with maximum flow rates of 10 and 50 ml/min are available. That could help to reduce air bubble generation. 5 mL/min c. 2 Set the flow of the pump at 1ml/min. 5:26. • Purge each channe lwtih 25–3m. The user manual for the Agilent G1311A Quaternary Pump, a high-performance liquid chromatography (HPLC) module that provides reliable gradient formation and precise flow rates. Turn off the pump by pressing "Pump" on the LC-20AD 4. Overall Routine Pump Maintenance 1. If problem persists, flush system with 100% methanol or isopropanol. Honoring the Past, Focusing on the Future: A Conversation with Jess Lee. Solving Problems That Matter - Bioprocessing. This installment is the first of a series of four white papers on high performance liquid chromatography (HPLC) modules (pump, autosampler, ultraviolet [UV] detector, and. Achieve binary-like performance in your HPLC instrument. This is needed to purge any air from the tubing, introduce fresh mobile phase to each line and then toHPLC, and biocompatible pumps. thermoscientific Vanquish Pump H VH-P10-A-02 Operating Manual 4820. And, remember, if you have a dual-piston pump, you have two piston seals to replace. Waters Second Quarter 2023 Highlights. The system guide, Waters doc# 71500269502, details. ID stainless steel tubing kit • Galaxie Chromatography Software-0. Residues or contaminations may block filters or capillaries. Purification Solvent Management. Two of the most widely used methods to degas a mobile phase are: Helium purging: helium is bubbled through the solvent and removes up to 80% of dissolved air. Replace piston seals. the purge valve, and the actual pump mechanism. Each page is marked with a tab and a footer to help you access information. Priming and Purging the 1525 Binary HPLC Pump. 5 um columns, use 0. Set a flow of 5 ml/min and purge each channel for 5 min with HPLC-quality Water. *Run to run RT variation of ±0. 19 Section 3: Pump Maintenance 20 Purge Valve 21 Outlet Ball Valve 21 Active Inlet Valve (AIV) 22 Seals and Pistons 25 Pump Head 26 Parts and Supplies 27 Solvent Inlet FiltersChromaster HPLC 5110 pump with auto-purge valve. Pump 15 minutes at this pressure to wear in the seals. 1. Press the purge buttons again to. If problem persists, flush system with 100% methanol or isopropanol. a Continue to purge for a short while. The manual covers the overview, installation, operation, and optimization of the pump, as well as troubleshooting and maintenance tips. It features an integrated pressure sensor, which ensures pressure-independent flow rate accuracy. Stop the pump and shut down software “HPL1(online)” f. Basic HPLC System Components. - after changing solvents. 5 ml/min for 4 min, I only collected 1 ml of liquid. Figure 2. Close the purge valve, set the flow to a value that gives a pressure of 350 bar. A damping unit is connected between the two plunger chambers. Purge the pump, check general functionality (for instance with a diagnostics test), read pre-compression value from pump panel and compare against values from manual (Thermo Scientific Dionex pumps only). Prime/Purge the pumps until no more air bubbles leave the pump heads. TapIn this technical article you will learn about the procedure for purging air from a reversed-phase column. With regular pump usage, this is recommended every six months. In other words is the system configuration comprising of the pump, injector/autosampler, column, and detector is appropriate for carrying out the analysis in. Open the purge valve and set the flow rate of 5 mL/min for each channel with HPLC grade water. Piston Housing of the Pump Head Assembly: The red arrows show the springs pushing back the pistons. If it does not, check the state of the Solvent Filters and replace them. Place the solvent bottle back into LC eluent. Relevant functions marked for purging, flow settings ect. 2 Low Pressure No/Low Pressure Reading Question Yes No 1. 4411-EN-2. L/mni for 5mni . 5:26. Prepare the Sampler • Avoid using needle wash and seat backflush with organic solvents with buffer applications, Most solvents need to be degassed, so U/HPLC systems typically include a solvent degassing system. Turn the black valve anticlockwise to purge the mobile phase. This video shows the operation a HPLC purge valve. 9. To manually purge the reference side of the 2414 flow cell, press the Shift + 1 button (Purge) on the screen while the pump is flowing mobile phase. Open prime/purge valve (in the case of Chrom Tech pumps, you turn the knob counterclockwise one to two turns. For short gradient delay times, the gradient delay volume can be reduced to less than 70 µL. with a new bottle of HPLC-grade water. Rough pumps stay on so the system remains under vacuum. 6. Replacing the Plunger Seal and Plunger. Replace the part that causes the obstruction. 1290 Infinity II High Speed Pump. Make sure that you know which solvent is linked to which pump. 8 Click pump on the flow diagram and change the flow path into A2 and B2. 1. Documents & Downloads. Open the Purge Valve by turning it counterclockwise b. • Mast kit with mixer, purge valves and manual injector • Pre-formed 0. The historical evolution of HPLC pumps and their characteristics has been reviewed in many textbooks (1–3), as well as journal articles (4–6). HPLC is an abbreviation for High Performance Liquid Chromatography. Otherwise, locate where the increased pressure is coming from. If you cannot see a leak at the bottom of the pump head when you try to purge, then most likely a leak is not the cause of the issue. Operation of DAD: [][]Switch ‘ON’ the power of Quaternary Pump, Autosampler, Thermostatic Column Compartment, Detector, CPU, Monitor if already not switched on. We have been experiencing some pressure problems on our hplc lately and the problem is mostly fluctuations in the pump head.