3.3 Valves, Fittings, Fitting Selection & Prohibited Connections

3.3 Valves, Fittings, Fitting Selection & Prohibited Connections

Quick Answer: A sanitary tee may be used for a horizontal-to-vertical change of direction only (IPC 2018 Table 706.3); it is not permitted vertical-to-horizontal or horizontal-to-horizontal. On the supply side, IPC 606.1 names eight locations where a full-open valve is required, including the water service near the curb, the discharge side of every water meter, the entrance to each dwelling unit, and the supply to every water heater.

Valve and fitting items reward candidates who understand why the code cares. A valve must isolate a section of work without strangling flow through it. A drainage fitting must turn the flow without letting waste fall free, pile up against a shoulder, or siphon the trap opposite it.

Full-open valves versus shutoff valves

The IPC uses two distinct terms and the exam tests the difference. A full-open valve is defined in IPC Chapter 2 as a water control or shutoff component in the water supply piping which, adjusted for maximum flow, presents no restriction in the component's through-flow area. A gate valve, a full-port ball valve and a butterfly valve satisfy that. A globe valve — whose disc seats against a horizontal seat and forces water through a reversing, S-shaped path — does not. A plain "shutoff valve" carries no such requirement, so a globe pattern or an angle stop is acceptable wherever the code says only shutoff.

IPC 606.1 — where full-open valves are required

1. On the building water service pipe from the public water supply, near the curb
2. On the water distribution supply pipe at the entrance into the structure
3. On the discharge side of every water meter
4. On the base of every water riser pipe, in occupancies other than one- and two-family dwellings and multiple-family residential occupancies two stories or less in height
5. On the top of every water down-feed pipe, in occupancies other than one- and two-family dwellings
6. On the entrance to every water supply pipe to a dwelling unit, except where it supplies a single fixture equipped with individual stops
7. On the water supply pipe to a gravity or pressurized water tank
8. On the water supply pipe to every water heater

IPC 606.2 — where shutoff valves are required

1. On the fixture supply to each plumbing fixture, other than bathtubs and showers in one- and two-family residential occupancies, and other than individual sleeping units already provided with unit shutoff valves in hotels, motels and boarding houses
2. On the water supply pipe to each sillcock
3. On the water supply pipe to each appliance or mechanical equipment

IPC 606.3 requires access to all full-open and shutoff valves. IPC 606.4 requires service and hose bibb valves to be identified, along with any valve installed away from the fixture or appliance it serves.

Choosing the right valve for the service

IPC 605.7 requires valves to be compatible with the piping material installed, to conform to one of the standards listed in Table 605.7 or be approved, and — where they supply drinking water — to meet NSF 61. Fittings are governed separately by IPC 605.5 and Table 605.5, and also carry the NSF 61 requirement in water supply systems; manufactured pipe nipples fall under 605.8. Two PRV details are frequently tested: 604.8.1 requires the valve to be designed to remain open on failure so supply is not interrupted, and 604.8.2 requires it to be installed so parts can be repaired or removed without breaking the pipeline. Separately, 604.9 requires a water-hammer arrestor conforming to ASSE 1010 wherever quick-closing valves are used.

Why valve choice is really a sizing decision

Appendix E of the IPC publishes friction allowances expressed as equivalent lengths of pipe. For 1-inch threaded components:

Take a 1-inch run with four 90-degree elbows and one isolation valve. With a gate valve the fitting allowance is 0.6 + (4 x 3.0) = 12.6 feet. Substitute a globe valve and the identical run becomes 25.0 + 12.0 = 37.0 feet — nearly triple the friction from a single component, and 25.0 / 0.6 = about 42 times the loss of the gate valve on its own. That is precisely why the code writes "full-open" wherever a valve exists to isolate rather than to throttle.

Drainage fittings: geometry first

Drainage bends are named as fractions of a full circle, which is all the geometry the exam expects:

A short sweep and a long sweep are both quarter bends; the long sweep has the larger radius and the gentler entry. Sanitary tee, wye, and combination wye and eighth bend are branch fittings, and it is the pattern of flow they create — not the name on the carton — that decides where they may be used. IPC 706.3 states the governing principle in one sentence: fittings shall be installed to guide sewage and waste in the direction of flow.

Table 706.3, Fittings for Change in Direction (IPC 2018)

(a) The fittings shall only be permitted for a 2-inch or smaller fixture drain. (b) Three inches or larger. (c) For a limitation on double sanitary tees, see Section 706.3.

Read the table as three questions asked in order: which way does flow enter, which way does it leave, and how big is the pipe? The sanitary tee is the pattern that trips candidates. Its branch has a short radius, which is harmless when gravity is already pulling waste down a stack (horizontal to vertical), but produces a near-square corner when flow must be turned out of a vertical fall or across a horizontal run — hence the two blank cells.

Watch how the footnotes interact on the short sweep, vertical-to-horizontal row, which carries both (a) and (b): the fitting is acceptable where the fixture drain is 2 inches or smaller, or where the piping is 3 inches or larger. Long sweeps, wyes, and combination wye-and-eighth-bend fittings carry no footnote at all, which makes them the safe answer for a vertical-to-horizontal turn at the base of a stack.

Section 706.3 also reaches combination fittings, side inlets and increasers: each is judged against Table 706.3 "based on the pattern of flow created by the fitting," so an increaser used to change direction is evaluated by the shape the water actually sees.

Double sanitary tees

A double sanitary tee pattern shall not receive the discharge of back-to-back water closets, or of fixtures and appliances with pumping-action discharge. The single exception is numeric and heavily tested: back-to-back water closet connections to a double sanitary tee are permitted where the horizontal developed length between the outlet of the water closet and the connection to the double sanitary tee pattern is 18 inches (457 mm) or greater. That distance is what keeps one bowl's flush from siphoning the bowl opposite.

Heel- and side-inlet quarter bends

IPC 706.4 is three short sentences, each a potential exam item:

• Heel-inlet quarter bends are an acceptable means of connection, except where the quarter bend serves a water closet.
• A low-heel inlet shall not be used as a wet-vented connection.
• Side-inlet quarter bends are an acceptable means of connection for drainage, wet venting and stack venting arrangements.

Notice that 706.4 is mostly a permission. This is where candidates trained on the Uniform Plumbing Code lose points, because the UPC lists side-inlet quarter bends among its prohibited drainage fittings. Maryland adopts the IPC.

No reduction in the direction of flow

IPC 704.2 prohibits reducing the size of drainage piping in the direction of flow. Three arrangements are expressly not treated as reductions: a 4-inch by 3-inch water closet flange; a water closet bend fitting with a 4-inch inlet and a 3-inch outlet, provided the 4-inch leg is upright and below the closet flange (it need not connect directly to it); and an offset closet flange.

IPC 706.2 adds that fittings shall have no ledges, shoulders or reductions capable of retarding or obstructing flow, and that threaded drainage pipe fittings shall be of the recessed drainage type. That is why an ordinary threaded pipe tee, whose internal shoulder catches solids, is never a drainage fitting.

Prohibited joints and connections

IPC 707.1 prohibits exactly six things in sanitary drainage:

1. Cement or concrete joints
2. Mastic or hot-pour bituminous joints
3. Joints made with fittings not approved for the specific installation
4. Joints between different diameter pipes made with elastomeric rolling O-rings
5. Solvent-cement joints between different types of plastic pipe, except as provided in Section 705.16.4
6. Saddle-type fittings

The 705.16.4 exception is narrow. A solvent-cemented ABS-to-PVC joint is permitted only as a single joint at the end of the building drainage pipe and the beginning of the building sewer, using a solvent cement complying with ASTM D3138. Everywhere else, dissimilar plastics require an approved adapter fitting, and plastic to cast-iron hub pipe is joined with a caulked joint or a mechanical compression joint.

On the water side, IPC 605.9 carries a shorter four-item list: cement or concrete joints, joints made with fittings not approved for the specific installation, solvent-cement joints between different types of plastic pipe, and saddle-type fittings.

Exam Trap: The favourite distractor is the side-inlet quarter bend, offered as a prohibited fitting. Under IPC 2018 it is expressly permitted for drainage, wet venting and stack venting by Section 706.4. The same trap runs through prohibited-joint items: running threads, bands and saddles are all banned drainage fittings under the Uniform Plumbing Code, but only the saddle appears on the IPC's six-item list at 707.1. Answer from the book in your hand. And never soften a blank cell in Table 706.3 into "permitted if you use a long-radius fitting" — the sanitary tee has no vertical-to-horizontal or horizontal-to-horizontal use at any pipe size.