Wastes, overflows, and rain-pipes from the house drain may cause issues even if it is perfectly constructed. Some authorities advise disconnecting soil-pipes of water-closets and slop-sinks as well. It's necessary in some positions but generally a main soil-pipe acts better and safer as a direct connection to the private drain. The intercepting trap shown here provides means for emptying manhole chambers through raking eye arrangement if there is a stoppage causing backing up of drainage. A chain attached to air-tight stopper releases it, opening communication directly with outer drain to clear flooded chamber. In some positions, perfectly air-tight manhole cover is extremely important. Fig. 73 shows coverplate screwed down by gun-metal bolts outside rubber ring making the cover reliably secure and gas-tight. Fig. 74 has inner cover arched for condensing moisture from drain-air with water running into groove maintaining constant seal. Top cover is flat fitting another groove which may be independently staunched. Traffic over top cover thus cannot affect inner cover or its seal.<Callout type="important" title="Critical Design">The design of the manhole chamber cover must ensure it remains gas-tight and secure, preventing any sewer gases from entering the house.</Callout>
Illustration of all interceptor trap patterns is impractical due to variety. We select some test forms. Fig. 75 shows a 6-inch interceptor with drainage falling on water-seal but small lip for throwing drainage clear of back may cause obstruction and are objectionable. A 6-inch trap is generally too large for ordinary houses. Fig. 76 illustrates smaller scale, better size less likely to choke up due to every flush thoroughly scouring it. Notice slope given top affording easy access for fresh air inwards.<Callout type="tip" title="Pro Tip">A 4-inch interceptor is a better size and less prone to clogging compared to the larger 6-inch models.</Callout>
Fig. 77 shows another form useful when connecting 4-inch house drain with 6-inch outfall drain. Trap itself and inlets are four inches, best size for ordinary dwellings; while outgo is six inches saving need for reducing piece connection with 6-inch drain.<Callout type="risk" title="Risk of Freezing">In cold positions, traps like Fig. 78 expose water-seal more than necessary to danger of freezing in winter.</Callout>
Fig. 81 shows an excellent arrangement for complete disconnection of subsoil drains with channel left open or covered by very open grating. Care must be taken to prevent slops passing into the open channel when used for subsoil-drain disconnection.<Callout type="beginner" title="For Newbies">Disconnectors for bath and trough wastes may be smaller than interceptors but should not connect directly to drains.</Callout>
Key Takeaways
- Interceptor traps are crucial for preventing sewer gases from entering the house.
- Proper design of manhole chamber covers is essential to maintain a gas-tight seal.
- A 4-inch interceptor trap is generally more effective and less prone to clogging than larger models.
Practical Tips
- Ensure all manhole chambers have reliable, air-tight covers to prevent sewer gases from entering the house.
- Use smaller diameter interceptors for better performance and reduced risk of blockages.
- Install vent pipes leading directly up from the front area of the house to ensure proper ventilation.
Warnings & Risks
- Avoid unnecessary inner projections in interceptor traps as they can cause obstructions and are generally undesirable.
- In cold climates, be cautious with water-seal designs that expose them excessively to freezing conditions.
Modern Application
While this chapter focuses on early plumbing systems from the early 20th century, many of its principles remain relevant today. Proper design and installation of interceptor traps and manhole chambers are still crucial for maintaining sanitary drainage systems in modern homes. The emphasis on preventing sewer gases from entering living spaces is as important now as it was then.
Frequently Asked Questions
Q: What is the purpose of an intercepting trap?
The intercepting trap provides a means to empty manhole chambers through a raking eye arrangement in case of stoppage causing backing up of drainage. A chain attached to the air-tight stopper releases it, opening communication directly with outer drain.
Q: Why is a 4-inch interceptor better than a 6-inch one?
A 4-inch interceptor is less likely to choke up compared to larger models because every flush thoroughly scours the trap. It's also more suitable for ordinary dwelling houses.
Q: What precautions should be taken when using interceptors in cold climates?
In cold positions, traps expose water-seal more than necessary to danger of freezing in winter. Therefore, it is important to design the trap such that the water seal is not overly exposed.