Drain holes

All tray sections, draw-off sumps, recessed downcomer inlet sumps, seal pans, chimney trays, and other tower internals must be selfdraining. As a column is heated on start-up, water can expand to steam with explosive force. Especially for lower pressure and larger diameter towers, tray panels are frequently dislodged due to flashing of trapped water. My experience indicates that drain holes of less than 0.5 inch, drilled in the bottom of a pan are likely to plug off due to fouling. The better way to place a drain hole is in a vertical wall of a pan, flush with the pan floor, as indicated in Fig. 9.3. 

Chimney draw-off trays are typically designed to slope toward the draw-off nozzle, thus avoiding a need for drain holes. However, with age, such trays warp because of thermal expansion and pools of water can be trapped. Inspection after water washing will reveal such poorly drained trays and pinpoint the location of required drain holes. But excessive use of drain holes can also be bad. Product losses through the drain holes can be estimated by the following  

The volumetric rate of flow lost through the drain hole is then the hole area multiplied by the hole velocity. With this equation in hand, your inspection may find drain holes that are best closed. 

If a drain hole plugs on a bottom tray seal pan, I have found that the seal pan will, with time, fill with dirt and corrosion products. This restricts the flow from the downcomer and has caused at least one amine fuel gas hydrogen sulfide absorber to flood. To avoid this problem. I ll size the drain holes in such seal pans to pass 20 percent of the liquid flow, or at least use a single 1-inch drain hole. Unless liquid is flushed out of the bottom of the bottom tray seal pan, the solids washed down the column settle out in the seal pan. 

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This test is prescribed by ANSI C-37/20C for isolated phase bus systems after they have been assembled at site. The test is conducted by filling the enclosure with air up to a pressure of 15 cm of water (1500 N/m ). After the air supply is shut off, the pressure must not drop to less than 7,5 cm of water in 15 seconds. All breathers and drain holes must be sealed before the test. 

CRANKSHAFT OIL SEAL LEAKS 1. Faulty seal installation. 2. Clogged drain hole. 

Relief valves vented to the atmosphere should have tail pipes equal to or larger in diameter than the relief valve outlet that extend vertically a minimum of one foot above building eaves, or eight feet above adjacent platforms on operating areas. The tail pipes should be provided with a drain located such that the exhaust through the drain hole does not impinge on vessels, piping, other equipment or personnel. 

Figure 10-4 shows what happened to the tailpipe of a steam relief valve that was not adequately supported. The tailpipe was not provided with a drain hole (or if one was provided, it was too small), and the tailpipe filled with water. When the relief valve lifted, the water hit the curved top of the tailpipe with great force. Absence of a drain hole in a tailpipe also led to the incident described in Section 9.2.1 (g). 

On other occasions, drain holes have been fitted in relief-valve tailpipes even though the relief valve discharged into a flare system. Gas has then escaped into the plant area. 

Drain holes in relief valve tailpipes. If they choke, rainwater will accumulate in the tailpipe (see Section 10.4). 

If inlet weirs are used they should have at least two slots %-in. by 1-in. flush with the tray floor to aid in flushing out any trapped sediment or other material. There should also be weep or drain holes below the downcomer to drain the weir seal area. The size should be set by the type of service, but a minimum of M-in. is recommended. 

A steam-water separation device consisting of a horizontal closed pipe, perforated at the top and with drain holes at the bottom. 

Holes should discharge from the bottom or bottom half of the distributor pipe so that they can serve also as drains for liquid. Separate drain holes may be needed for the manifold pipe and in each distributor pipe. 

Adapters (Figure 1) were designed to plug into the drain holes at the bottom of the cultivation pot. The adapters were made of acetal plastic and had caps with silicone septa of the same type as used in gas... 

The floor should be pitched toward drain holes to prevent accumulation of liquids. 

A. Commercial potting soil will do. Make sure the pot is large. It should have a drain hole. Placing gravel (or broken up chunks of styrofoam) in the bottom of the pot will help promote drainage and thus discourage root rot. 

Laboratory lysimeters were constructed of plexiglass tubing (6.2 cm i.d. 0.6 cm wall thickness 90 cm length), supported in a vertical position. A 164 micron pore size corundum disc (6.10 cm diameter 0.6 cm thickness) was placed in each column directly over the drain hole in order to support the fly ash sorbent and to prevent clogging of the outlet. 

For liquids with entrained gas or vapor, a "vent hole" should be provided, and for gases with entrained liquid, a "drain hole." Meters for liquid with entrained gas or gas with entrained liquid services should be installed vertically. Normally, the flow direction would be upward for liquids and downward for gases. The use of vent and drain holes is discouraged, if in order to keep them from plugging, the holes would need to be large and would adversely affect accuracy. On severe entrainment applications, eccentric or segmental orifice plates should be used. 

When DNA has formed a tight ball, carefully remove supernatant using a Pasteur pipet attached to a water vacuum pump the outflow of which is piped directly into the sink drain hole to avoid splashing. Do not be concerned about tiny fragments of DNA being sucked down the sink but do avoid the bulk of the DNA It is possible to remove all of the supernatant safely in this way. 

The ideal chemical process is that which a one-armed operator can perform by pouring the reactants into a bath tub and collecting pure product from the drain hole. 

During shutdown, it is necessary to drain the trays and seal pans of unevaporated liquid and steam condensate. At least two drain holes are needed for each tray or seal pan, at 0.50 in. minimum diameter and preferably 0.75 in. to avoid plugging. As a rule of thumb, a 0.75 in. hole will deliver about 2gpm of liquid during tower drainage. 

Drain. Bearing housing shall be provided with tapped and plugged drain hole at its lowest point. When replacement grease is specified, a means for grease relief shall be provided. 

It is sometimes possible to use judiciously placed drain holes to create a preferred flow path for subsequent grouting. Such procedures were used to control seepage into the underground portion of a grain silo, in a job done by Denver Grouting Services, Inc. 

Figure 4.36 shows some recommended dimensions (289) for a vapor space sparger. Drain holes are required if the bottom of the sparger is unperforated. Guidelines 2 and 4 in Sec. 4.1, and guidelines 1, 3 to 9, 11, and 12 in Sec. 2.4 also apply to vapor space spargers. In packed columns, it was recommended (289) to restrict perforation pressure drop to less than 1 psi. 

Drain holes should be drilled through the bottom of the inlet weir to enable liquid drainage at shutdowns. 

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