Engineers are showing less detail on the drawings for valves, strainers, pressure gauges, temperature gauges and other piping accessories. They are showing less information on the plans, and they are describing the piping accessories in the specifications to cover all of the accessories required for a given branch or piece of equipment in the piping system.
In today’s competitive environment engineers are showing less information on the drawings and cover piping accessory items in the specifications. The competition between design firms has caused firms to find ways to save time producing drawings and specifications. Many firms have resorted to showing the piping to a piece of equipment as general routing without showing valves, gauges, fittings or other accessories on the plans.
The industry standard seems to be to show the equipment in a detail on the drawings where valves, gauges, thermometers and other accessories are shown for each piece of equipment. This trend has been developing for the design of commercial, industrial and institutional facilities, unless an owner has their own design standards. Such a trend is possible because the commercial, industrial and institutional industries do not have industry-wide design standards or guidelines for mechanical systems like the military, large corporations or government agencies.
A recent trend has been for many design firms to switch to 3D files using Revit, AutoCad MEP or another 3D CAD software program to show more detail in the piping system. Not all firms are showing all of the valves and accessories. Some firms show the piping and the general routing, but they are not showing the valves, accessories or even pipe hangers. They typically call for branch valves, strainers, gauges, thermometers, etc. at locations described in the specifications rather than showing them on the drawings. While this saves time for the engineer, it creates confusion and a wide discrepancy during the bidding process and construction.
Specifying the locations for the accessories in the specifications makes it very difficult for a contractor to get an accurate count of isolation valves and other accessories during the bidding phase. Mechanical and plumbing contractors are often faced with adding valves, strainers, pressure gauges, thermometers and many other accessories after the piping system is installed.
When there are little or no accessories shown on the plans, it leaves many items subject to interpretation. Engineers have been known to include catchall notes on the plans or in the specifications that call for isolation valves to be located in an accessible location near all branch take-offs from piping mains. The problem with the catchall note is only the engineer can tell you where the accessible location is. Accessible to the contractor may mean accessible from a ladder, accessible to the engineer, or owner may be 3 feet from the ground. If the valves and accessories are shown on the plans, there is no question where they go.
When an owner does not request and pay for field representative services to assure the system is built properly during construction, these accessories can be omitted and not noticed or missed until something goes wrong. When a piece of equipment needs service there needs to be a way to isolate that piece of equipment and there should be valves off of the mains at key locations to prevent shutting down the entire building to perform service on a piece of equipment.
Pumps should have accessible isolation valves on the suction and discharge pipes with pressure gauges between the pump and the shut-off valves. The pressure gauge specifications should include gauge cocks and snubbers to prevent the pulsations from the pump impellers from vibrating the gauge needle. Snubbers or impulse dampeners make reading the pump easier and they can extend the life of the gauges.
Base mounted pumps often need flow straighteners or suction diffusers because elbows close to the pump create turbulence that can reduce pump performance. Flow straighteners create laminar flow at the pump suction and improve pumping efficiency. Flexible connections with inertia pads and vibration isolator springs prevent sound transmission to the building and the piping system. The discharge pipe should have a check valve and in some cases a throttling valve for flow control.
In the case of larger pumps a triple-duty valve can serve as a combination check valve, throttling valve, and shut-off valve on the discharge of the pump. Smaller in-line pumps should have unions or flanges on each side of the pump to allow for removal for servicing. Larger pumps should have mechanical connections or flanged connections to allow for removal and pump servicing.
Consideration should be given to pump location for maintenance. Motors and control panels have clearance requirements spelled out in the National Electric Code, Published by the National fire Protection Association (NFPA). The motor and control panel voltages determines the clearance required around a pump and control panel.
Water heaters and heat exchangers
Water heaters and heat exchangers should have isolation valves to allow for maintenance they should also have unions or flanges to allow for removal of the heater without cutting and reworking of the piping. There should be thermometers on the inlet and outlet of a water heater or heat exchanger to be able to see how it is performing.
Pressure and temperature relief valves should be sized in accordance with the rated capacities of the equipment. When recirculating pumps are connected to water heaters make sure there are check valves to prevent reversal of flow. Pressure gauges should be located on the inlet and outlet of heat exchangers to indicate clogging or fouling of the heat exchanger tubes. They can also show pressure increases associated with thermal expansion. Water heaters and heat exchangers should have expansion tanks to absorb thermal expansion.
All accessories critical to the operation and maintenance of the system should be shown on the drawings. At least make sure the accessories are shown on the details of the equipment.
Typically, the piping accessories are specified in the specification section titled, “Piping Specialties.” When specifying the pressure gauges, be sure to give the pressure range and or vacuum range expected for the gauges. The system’s normal operating pressure should be in the gauge’s mid-range. The size of the gauge face should be specified so it can be read easily from the mechanical room floor.
The most common sizes of the dial faces are 3 inches through 6 inches in diameter, although other sizes are available. As a general rule of thumb, the larger the dial face the more expensive the gauge. Make sure the gauge suits the application. When specifying thermometers make sure there are thermometer wells for the thermometers and specify the type of thermometer liquid filled glass bulb type or dial type thermometers. Specify the temperature range for the thermometer so that it will read in the middle of the thermometer and cover the expected high and low temperatures expected in the system.
Pipe supports are covered in Section 308 of the International Code. When the pipe support spacing requirements from a manufacturer differ from the spacing requirements in the code, the more stringent requirements should apply. IPC 2012 section 301.7
In instances where conflicts occur between this code and the manufacturer’s installation instructions, the more restrictive provisions shall apply.
Ron George, CPD, is president of Plumb-Tech Design & Consulting Services LLC. The offices of Ron George, CPD, have relocated to 303 N. Monroe Street, Monroe, Mich., 48162. The phone numbers and website will remain the same: Office 734-322-0225; Cell Phone: 755-1908; and Website: www.Plumb-TechLLC.com.