Low point

Provide provision for drainage of ducts (e.g., sloped, low point drains)... 

Design vent lines to prevent low point traps (pockets)... 

For several years now, cable ducts have been manufactured from plastic pipes, which are watertight and form a continuous run of piping. In laying the ducts, low points can occur in which condensed water or water penetrating from the ends can collect. In many cases this water has led to corrosion damage in lead-sheathed cables. Lead-sheathed cables must therefore only be used in such ducts with an additional PE sheath of type A-PM2Y. Cathodic protection of these cables is not possible because of their complete insulation by the plastic pipe. 

Drains shall be provided at the low points of the inlet easing and be at least 1.5 in. in size. Class 300. 

Locate leaks Apply soap solution to tape bleed holes and threaded connections depressure when tests are done. Block in N2 and check for loss of pressure. Check all connections. Same as in Step 1. Tag flanges to identify leaks tighten or repair leaks each time a system is pressurized, drain condensate at low-point bleeds. 

Subsurface drains are essentially permeable barriers designed to intercept the groundwater flow. The water must be collected at a low point and pumped or drained by gravity to the treatment system (Figure 8). Subsurface drains can also be used to isolate a waste disposal area by intercepting the flow of uncontaminated groundwater before it enters into a contaminated site. 

This section covers low point drains and high point vents, as well as connections... 

The elevation of gravity drain systems must be carefully checked to assure that liquids will flow to the collection point without exiting the piping at an intermediate low point. 

At high points in piping, vent valves are required to remove air for hydrotesting and for purging the system. At low points, drain valves are required to drain liquids out of the system to perform maintenance. Normally, vent and drain valves are 14-in. or i-in. ball valves. 

To prevent the accumulation of moisture in conduits and enclosures, drains should be installed at all low points. In classified areas, breathers and drains must be explosion-proof. Figure 17-28 shows typical explosion-proof breathers and drains. 

When possible, drain points in a pipeline should be fitted at low points, and slip-plates should be fitted at high points. 

When two atoms approach each other so closely that their electron clouds interpenetrate, strong repulsion occurs. Such repulsive van der Waals forces follow an inverse 12th-power dependence on r (1/r ), as shown in Figure 1.13. Between the repulsive and attractive domains lies a low point in the potential curve. This low point defines the distance known as the van der Waals contact distance, which is the interatomic distance that results if only van der Waals forces hold two atoms together. The limit of approach of two atoms is determined by the sum of their van der Waals radii (Table 1.4). 

Tief-ofen, m. (Metal.) soaking pit. -punkt, m. low point, mimmum point. 

Holes for drainage must be adequate to drain the column in a reasonable time, yet not too large to interfere with tray action. Draining of the column through the trays is necessary before any internal maintenance can be started or before fluid services can be changed, when mixing is not desirable. The majority of holes are placed adjacent to the outlet or downcomer weir of the tray. However, some holes are placed in the downcomer inlet area or any suspected low point in the mechanical layout of the column. 

Oil is not a real problem in centrifugal machines, except that its carry-through affects condensation in the condenser. In an ammonia system, the oil will setde out and can be purged from low points of the system, as receiver, evaporator, etc. 

Adequate ventilation is provided by means of openings at the top of high points and the bottom of low points. These openings shall have a free open area of 1/150 of the cross-section area of the duct or 0.05 m, whichever is the greater. 

These are not normally required. Where wet gas is supplied, it will be necessary to fit a vessel at low points in the installation to collect any condensate or fluid. This vessel shall be in a readily accessible position and a valve, suitably plugged or capped, shall be fitted to its drain connection. In the exceptional case where hydraulic pressure testing is to be carried out, similar provisions must be made. 

Before piping is installed, the layout should be analyzed to eliminate low points where liquid could collect and to provide drains where low points cannot be eliminated. A regular part of the operating procedure must be the periodic drainage of low points in the piping and separators, as well as inspection of automatic drain traps. 

Ideally, the sample should be taken from a valve installed specifically for sampling. When sampling valves are not installed the taking of samples from locations where sediment or water can collect, such as dead ends of piping, tank drains, and low points of large pipes and filter bowls, should be avoided if possible. If samples are taken from pipe drains, sufficient fluid should be drained before the sample is taken to ensure that the sample actually represents the system. Samples are not to be taken from the tops of... 

With ammonia, oil sinks to the bottom and does not go into solution with the refrigerant. Ammonia condensers, receivers and evaporators can be distinguished by the provision of oil drainage pots and connections at the lowest point. Automatic drainage and return of the oil from these would have to depend on the different densities, and is veryrarely fitted. The removal of oil from collection pots and low-point drains is a periodic manual function and is carried out as part of the routine maintenance. The halocarbons are all sufficiently miscible with oil to preclude the possibility of separate drainage in this way. 

Removal of condensation is an important consideration. Water collecting in an elbow or other low point of the system can effectively block the pipe, and reduce or disable the system. Builders should strive to design a pipe system that will allow condensation to run back through the pipe to the subslab aggregate. This can be accomplished by ensuring that the pipe run is vertical to the entire distance from the basement to the exhaust. A completely vertical pipe run with no bends or elbows will also provide a pipe system with lower static pressure losses that will enhance the effectiveness of both active and passive systems. If elbows or a low point is incorporated into the... 

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