Water pressures

Failure of water pressure can spell disaster in laboratories where some operations, such as distillations, are dependent on water. Ideally, an audible alarm would indicate the lack of water pressure. Laboratory supply houses sell water flow indicators that can be placed in series with the water line to equipment. When water is flowing, a brightly colored ball in a clear tube will move or a small propeller will turn. These can be observed from a considerable distance by watchful laboratory personnel. 

A gas failure is rare but could present a serious hazard if it should occur. Unless turned off, a gas-powered piece of equipment will pour unburned gas into the room after service has been restored. 

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In a normal pressure regime the pressure in a hydrocarbon accumulation is determined by the pressure gradient of the overlying water (dP / dD), which ranges from 0.435 psi/ ft (10 kPa/m) for fresh water to around 0.5 psi/ft (11.5 kPa/m) for salt saturated brine. At any depth (D), the water pressure (PJ can be determined from the following equation, assuming that the pressure at the surface datum is 14.7 psia (1 bara) ... 

The water pressure gradient is related to the water density (p, kg/m ) by the following equation ... 

If a pressure measuring device were run inside the capillary, an oil gradient would be measured in the oil column. A pressure discontinuity would be apparent across the interface (the difference being the capillary pressure), and a water gradient would be measured below the interface. If the device also measured resistivity, a contact would be determined at this interface, and would be described as the oil-water contact (OWC). Note that if oil and water pressure measurements alone were used to construct a pressure-depth plot, and the gradient intercept technigue was used to determine an interface, it is the free water level which would be determined, not the OWC. 

Water pressure at spraying nozzles and flow-rates. 

The high-pressure water supply service is employed for the operation of the ordinary filter pump, which finds so many applications in the laboratory. A typical all metal filter pump is illustrated in Fig. 11, 21, 1. It is an advantage to have a non-return valve fitted in the side arm to prevent sucking back if the water is turned off or if the water pressure is suddenly reduced. Theoretically, an efficient filter pump should reduce the pressure in a system to a value equal to the vapour pressure of the water at the temperature of the water of the supply mains. In practice this pressure is rarely attained (it is usually 4 10 mm. higher) because of the leakage of air into the apparatus and the higher temperature of the laboratory. The vapour pressures of water at 5°, 10°, 15°, 20° and 25° are respectively 6-5, 9-2,12-8, 17 5 and 23 8 mm. respectively. It is evident that the vacuum obtained with a water pump will vary considerably with the temperature of the water and therefore with the season of the year in any case a really good vacuum cannot be produced by a filter pump. 

The technique of the filtration of hot solutions has already been described in Section 11,28. The filtration of cold solutions will now be considered this operation is usually carried out when it is desired to separate a crystalline solid from the mother liquor in which it is suspended. When substantial quantities of a solid are to be handled, a Buchner funnel of convenient size is employed. The ordinary Buchner fimnel (Fig. 11,1, 7, a) consists of a cylindrical porcelain funnel carrying a fixed, flat, perforated porcelain plate. It is fitted by means of a rubber stopper or a good cork into the neck of a thick-walled filtering flask (also termed filter flask, Buchner flask or suction flask) (Fig. 11,1, 7, c), which is connected by means of thick-walled rubber tubing (rubber pressure tubing) to a similar flask or safety bottle, and the latter is attached by rubber pressure tubing to a filter pump the safety bottle or trap is essential since a sudden fall in water pressure may result in the water sucking back. The use of suction renders rapid filtration possihle... 

Schematic diagram of a piston corer in operation. The weight of the corer is sufficient to cause its penetration into the sediment, while the upward motion of the piston allows water pressure to help force the sediment column into the barrel of the corer.

This principle is illustrated in Figure 10 (45). Water adsorption at low pressures is markedly reduced on a poly(vinyhdene chloride)-based activated carbon after removal of surface oxygenated groups by degassing at 1000°C. Following this treatment, water adsorption is dominated by capillary condensation in mesopores, and the si2e of the adsorption-desorption hysteresis loop increases, because the pore volume previously occupied by water at the lower pressures now remains empty until the water pressure reaches pressures 0.3 to 0.4 times the vapor pressure) at which capillary condensation can occur. 

Direct water spray cooling must be carried out with care. The spray chamber must be designed to ensure complete evaporation of all Hquid droplets before the gas enters the baghouse. Spray impinging on the chamber walls can result ia a dust mud iaside the chamber and any increase ia gas dewpoint may result in baghouse problems or atmospheric plume condensation. Spray nozzle wear can result in coarse or distorted spray and wetted bags, and water pressure failure can cause high temperature bag deterioration. 

The term aquifer is used to denote an extensive region of saturated material. There are many types of aquifers. The primary distinction between types involves the boundaries that define the aquifer. An unconfined aquifer, also known as a phraetic or water table aquifer, is assumed to have an upper boundary of saturated soil at a pressure of zero gauge, or atmospheric pressure. A confined aquifer has a low permeabiUty upper boundary that maintains the interstitial water within the aquifer at pressures greater than atmospheric. For both types of aquifers, the lower boundary is frequendy a low permeabihty soil or rock formation. Further distinctions exist. An artesian aquifer is a confined aquifer for which the interstitial water pressure is sufficient to allow the aquifer water entering the monitoring well to rise above the local ground surface. Figure 1 identifies the primary types of aquifers. 

Water resistance test methods include AATCC 127 (hydrostatic pressure test), AATCC 42 (impact penetration test), and AATCC 35 (rain test). In the hydrostatic pressure test, a sample is subjected to a column of increasing water pressure until leakage occurs. The impact penetration test requires water to be sprayed on the taut surface of a fabric sample from a height of two feet. The fabric is backed by a blotter of predeterrnined weight, which is reweighed after water penetration. The rain test is similar in principle to the impact penetration test. 

The hydrostatic-pressure test is performed on fabric mounted under the orifice of a conical weU. The fabric is subjected to increasing water pressure at a constant rate until leakage occurs at three poiats on the fabric s undersurface. The rating is the height of the water head ia centimeters above the fabric (AATCC Test Method 127 INDA Standard Test 80.4-92). 

The third and perhaps most important class of water repellents consists of materials appHed to the surface of concrete for above-grade stmctures or others where water pressure on the concrete is small. This iacludes damp-proofing ia which treatments cannot be subjected to continuous or even intermittent hydrostatic pressure (83). Repellents that may be used are oils, waxes, soaps, resias, and siUcon-based systems (84). 

A 1990 study by American Cyanamid Co. demonstrated that the reaction cycle depends also on the supply pressure of the gaseous nitrogen. The 3-d reaction cycle at the normal 75 Pa (0.3-ia. water) pressure can be reduced to 2.4 d usiag the N2 gas pressure at 2 kPa (8-ia. water) iato the oveas (19). 

Performance Data for Direct-Heat Tray Dryers A standard two-truck diyer is illustrated in Fig. 12-48. Adjustable baffles or a perforated distribution plate is normally employed to develop 0.3 to 1.3 cm of water-pressure drop at the wall through which air enters the truck enclosure. This will enhance the uniformity of air distribution, from top to bottom, among the trays. In three (or more) truck ovens, air-reheat coils may be placed between trucks if the evaporative load is high. Means for reversing air-flow direction may also be provided in multiple-truck units. 

The test is carried out by washing down the test enclosures in every direction by means of a standard hose nozzle of 6.3 mm inside diameter, as illustrated in Figure 11.11, held at 3 m from the enclosure with a water pressure equal lo a head of nearly 3 m of water (— 30 kN/iiF), enough to give a delivery rate of 12.5 litres/min. The duration of Ihe lest will be determined at 1 min/m" of the surface area under test, subject lo a minimum of 3 minuies. 

The above water pressure will give a delivery rate of 100 litres/min. 

Coolant circuit water pressure and temperature (moisture) detection 12/307... 

The main part of the anode slurry, which can contain CaC03, depending on the hardness of the water, is chemically inert from the corrosion point of view, and settles to the bottom of the tank. The slurry must be removed once or twice a week through a stub with a stopcock this takes place in short bursts of opening and closing of the tap at full water pressure. The deslurrying outlet is at the end opposite to the water inlet in a horizontal tank. 

Source Pollutant Scrubber pressure loss and water pressure Flow rate... 

Hazard and risk explained. Control of Substances hazardous to Health Regulations 1988 (COSHH) Do you use a steam/water pressure cleaner You could be m for a shock ... 

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