Back-pressure Devices

Historically, bulk delivery systems have used manual diaphragm valves located at the return end of the global piping system, another carryover from high-purity chemical systems. However, the shear sensitivity of many slurries has fostered the creation of other baek-pressure approaches, including 

Pinch valves were introdueed in 1996 as an improvement in flow path compared to diaphragm valves. They have achieved some success, especially 

Pressure monitors at the return end of the global loop, coupled with active feedback to an adjustable valve have been used to compensate for fluctuations in line pressure. Unfortunately, the valves used have been diaphragm or needle valves, which have all of the shear challenges. While pressure consistency may be improved for the polishes nearest the control device, the shear challenge has not been addressed. Furthermore, the pressure fluctuation in the middle section of a global loop, as polishers turn on and off, can not be corrected by a device at the end. 

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The test procedure can be performed by pumping HPLC grade water at a specified flow rate under a controlled back-pressure, using a commercial back-pressure device connected in-line just after the pump. A f 000 psi back-pressure device is recommended. It is also advised that about f % MeOH be added to the water in order to minimize biological growth. While timing the process with a calibrated stop watch, the pump effluent should then be collected in a volumetric flask. From this, one can calculate the actual solvent flow at each flow rate. 

Note Do not use a commercial back-pressure device for this test, as this may dampen the true pressure pulsations arising from the pump. 

Note Experiments 1-4 are typically performed with a 1000 psi back-pressure device instead of a column. These tests should... 

Note After Experiment 4, one should switch the 1000 psi back-pressure device with a validated Cl8 column and adequately equilibrate the column with the appropriate mobile phase required for the subsequent experiment. The mobile phase solvents are usually percentages of methanol and water, depending on the chromatographic requirements for eluting the standard components that are used. 

Maximum pressure rating Back pressure device 540 bar... 

Treatment 1 Add 40-70psi back-pressure device to detector outlet line. 

Metal ion contamination, such as colloidal iron, can be released from frits, travel to other parts of the HPLC, and then be trapped. These types of contaminants will interfere with DNA in solution or after it has been released and trapped on a critical component of the H PLC such as the colurrui, an inline filter in front of the detector, or at a back-pressure device located after the detector. 

Attach a fine-bore (0.010 inch) piece of Teflon tubing (1/16 inch o.d.), about 0.5 m long to the flow-cell oudd. Calculate its internal volume in millilitres. Place its outlet in a conical flask. This tubing will serve as both a back-pressure device and a convenient directional tube, which is placed in separate containers as each faction is collected. 

Safety Relief Valve - A safety relief valve is an automatic pressure-relieving device suitable for use as either a safety valve or relief valve, depending on application. (In the petroleum industry it is normally used in gas and vapor service or for liquid.) Safety relief valves are classified as "Conventional" or "Balanced", depending upon the effect of back pressure on their performance. 

Superimposed back pressure The static pressure existing at the outlet of a pressure relief device at the time the device is required to operate. It is the result of pressure in the discharge system from other sources. 

Conventional relief valves should only be used where the discharge is routed independently to atmosphere, or if installed in a header system, the back-pressure build-up when the device is relieving must be kept below 10% of the set pressure so the set point is not significantly affected. The set point increases directly with back-pressure. 

Testing Procedures for Pressure Relieving Devices Discharging Against Variable Back Pressure... 

Back Pressure pressure existing at the outlet or discharge connection of the pressure-relieving device, result-... 

Verify critical pressure from Equation 7-7 and establish actual back pressure for relieving device. 

Testing Procedures for Pressure-Relieving Devices Discharging Against Variable Back Pressure, API-RP-525, American Petroleum Institute, New York, N.Y... 

P2 = back pressure or downstream at outlet of safety relief device, psig, or psia, depending on usage p = rupture pressure for disk, psig or psia p° = overpressure (explosion), lb force/sq in. p = pressure, psi abs... 

Back-pressure. Before the gases are vented to atmosphere, they might go through a device that has a pressure drop. This could be a heat recovery steam generator... 

Fig. 11 Extraction device consisting of A CO2 cylinder, B syringe pump, C oven, D extraction cell, E particle filter, F back-pressure regulator, G sampling tube...

Dissolved air flotation equipment is available from a number of manufacturers. Packaged units of steel construction are available with capacities to 7.6 cu m/min (2000 gpm). The essential elements of the DAF system are the pressurizing pump, air injection facilities, pressurization tank or contact vessel, back-pressure regulating device, and the flotation chamber [40]. 

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