Check valves, pumps

Amongst the many other applications for acetal resins should be mentioned links in conveyor belts, moulded sprockets and chains, blower wheels, cams, fan blades, check valves, pump impellers, carburettor bodies, blow-moulded aerosol containers and plumbing components such as valve stems and shower heads. 

POSSIBLE CAUSES Faulty pressure switch Leakage past check valve Pump damaged or worn Leaking past direction control valve or screen-changer cylinder REMEDY A Replace switch A Replace pump A Replace pump A Repair or replace... 

In a peristaltic pump, the volume of fluid displaced by the individual actuators is rectified, that is, directed in the desired direction of flow, solely by the phasing of multiple actuators. Other types of displacement pumps rectify flow differently. A passive check-valve pump uses two passive, one-way check valves incorporating moving flaps or other... 

Fig. 6. Homogenizer used as a timing pump for HTST pasteurization. Details of bypass, relief lines, equalizer, and check valves are not included (10).

Water. Water mains should be connected to plant fire mains at two or more poiats, so that a sufficient water supply can be deHvered ia case of emergency. The plant loop and its branches should be adequately valved so that a break can be isolated without affecting a principal part of the system. If there is any question of maintaining adequate pressure, suitable booster pumps should be iastaHed. Any connection made to potable water for process water or cooling water must be made ia such a manner that there can be no backflow of possibly contaminated water check valves alone are not sufficient. The municipal supply should faH freely iato a tank from which the water is pumped for process purposes, or commercially available and approved backflow preventers should be used. 

Reciprocating pumps are those most commonly used in high performance Ic. The single-piston type usually has inlet and outlet check valves with some mechanism such as variable stroke frequency to minimize the effect of pump pulsations. Dual-piston pumps operate with the pistons 180° out of phase to minimize pulsations. For this system to work optimally, the piston units must be identical. 

Unhke the control valve, the centrifugal pump has poor or nonexistent shutoff capabihty. A flow check valve or an automated on/off valve may be reqiiired to achieve shutoff reqiiirements. This requirement may be met by automating an existing isolation valve in retrofit apphcations. 

Install a positive-pressure steam (from nmuiug pump) to fill the suction line from the block valve through the check valve. 

Internal Re-circulation Operation / Design / Maintenance Internal Re-circulation results from something in the discharge side of the pump strangled valve, clogged filter, over-pressurized header, check-valve installed backwards. 

Third, you would. suppose that parallel pumps are identical, that they were manufactured and assembled together. But it is possible that one pump of the pair is the dominant pump and the other is the runt pump. If you start the dominant pump first in the parallel system, and then decide to add the runt pump of the pair, the weaker pump may not be able to open the check valve. The pump operator perceives that the flow meter on the second pump is stuck or broken. This is because the second pump might be dead heading against a closed check valve, maintained that w ay by the dominant pump. If this situation exists, it may re.sult in premature failure of bearings and. seals, leading maintenance and operations personnel thinking that parallel pumps are problematic. 

The solution is Identify the dominant and weak pump should they exist. To do this, take pressure gauge readings with the pumps running at shut-off head. Verify that the impellers are the same diameter, and that the wear bands and motor speeds are equal. If you can identify one pump in the pair as dominant, ahvays start the weak pump first and then add the dominant pump in parallel with the weaker. The dominant pump coming on stream w ill push open the check valve. It may be necessary to override a sequential starter. 

Check valves must be used on each pump discharge to prevent backflow through the idle pump. On those systems where a flooded suction is not furnished, an orificed bypass around the appropriate check valve should be furnished to keep the suction line of the non-flooded suction... 

Lubrication of cuuplitigs, Lubrication pumps. uid drivers, 309 Lubrication systems check valves, I commissioning, 462, 4ti coolers, 315 degassing drum, 322 filters, 316 gear box, 328 oil flooded helical, 109 overall system review, 1 overhead tanks, 319 piping, 322 pressure control valves, 313... 

After the fire, the check valves on all three pumps were found to be out of order. On one the seat had become unscrewed. On another the fulcrum pin was badly worn. On the third the pin was worn right through, and the flap was loose. The valves had not been inspected since the plant was built. 

If a pump trips (or is shut down and not isolated), it can be driven backward by the pressure in the delivery line and damaged. Check valves are usually fitted to prevent reverse flow, but they sometimes fail. 

In one plant, light oil was pumped at intervals from a tank at atmospheric pressure to one at a gauge pressure of 15 psi (1 bar). For many years the practice was not to close any isolation valves but to rely on the check valve in the pump delivery. One day a piece of wire got stuck in the check valve, oil flowed backward, and the atmospheric tank overflowed (Figure 18-4). 

A more serious incident occurred at a plant in which ethylene oxide and aqueous ammonia were reacted to produce ethanolamine. Some ammonia got back into the ethylene oxide storage tank, past several check valves in series and a positive pump. It got past the pump through the relief valve, which discharged into the pump suction line. The ammonia reacted with 30 m of ethylene oxide in the storage tank. There w as a violent rupture of the tank, followed by an explosion of the vapor cloud, which caused damage and destruction over a wide area [4],... 

By 1608 Captain Thomas Savery exploited these principles with a patented steam pump. Alternately admitting pressurized steam into a vessel forced water upward through a one-way (check) valve, while the... 

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