Integral vs External Vented Flow Control; How the Code Distinguishes Between Them

January 03, 2017

The Uniform Plumbing Code (UPC) provides requirements governing flow control devices for commercial grease interceptors. Confusion and subsequent questions are prolific enough to warrant a blog post to clear things up. Here you go. You're welcome.

Here is the verbiage contained in the Code that is confusing, "No flow control device having adjustable or removable parts shall be approved."

A few manufacturers of hydromechanical grease interceptors (HGI) use built-in or 'integral' flow controls. The challenge for Code readers is deciding whether the previous language applies to these devices or the exception in the Code, which reads, "Listed grease interceptors with integral flow controls or restricting devices shall be installed in an accessible location in accordance with the manufacturer's installation instructions."

First the short answer:

In the 2015 edition of the UPC, Section 1014.2 clearly identifies Type A and B hydromechanical grease interceptors and stipulates requirements governing the external flow control devices that are required for these devices in accordance with their certifications. The code adopted a definition of hydromechanical grease interceptors that is derived from the standard ASME A112.14.3, which distinguishes between four types of devices. Types A and B utilize an external flow control, with Type A requiring a vent on the flow control and Type B not. Types C and D are without external flow control, with Type C being directly connected and Type D being indirectly connected. Type C units normally come with a built-in or 'integral' flow control without an air intake (vent) and are exempted from the requirements that govern vented external flow controls in the exception, which states, "Listed grease interceptors with integral flow controls or restricting devices shall be installed in an accessible location in accordance with the manufacturer's installation instructions." 

Now for those of you who desire a more thorough explanation, take heart, I shall not disappoint you. 

Here is the long answer:

The 1948 edition of the UPC only defined one type of device called a 'grease interceptor' as, "a device for retaining grease or oil by gravity-differential separation from waste effluent and of a design and capacity approved by the Department having jurisdiction." The code introduced the requirement that, "every grease trap or interceptor, shall have an approved type flow control or restricting device installed in a readily visible location between the interceptor and each fixture connected thereto. All flow control devices shall be outside of, and not part of the interceptor, and so designed that the total flow through such device or devices shall at no time be greater than the rated capacity of the interceptor. No flow control device having adjustable or removable parts shall be approved." 

The 1952 edition of the UPC added the term 'grease trap' but defined both grease traps and grease interceptors as 'interceptors', which it defined as, "a device designed and installed so as to separate and retain deleterious, hazardous, or undesirable matter from normal wastes and permit normal sewage or liquid wastes to discharge into the disposal terminal by gravity." The code modified the requirements for flow controls on fixtures to clarify what was intended by stipulating, "each plumbing fixture or piece of equipment connected to any grease interceptor shall be provided with an approved type flow control or restricting device installed in a readily accessible and visible location in the tail piece or drain outlet of each such fixture. Flow control devices shall be so designed that the total flow through such device or devices shall at no time be greater than the rated capacity of the interceptor. No flow control device having adjustable or removable parts shall be approved." It is obvious that the requirements against adjustable or removable parts in flow control devices applied to those devices attached to the fixtures routed to a grease interceptor. 

The 1958 edition of the UPC changed the language from any grease interceptor to now say "a" grease interceptor. 

The 1982 edition of the UPC adopted new definitions for grease traps and grease interceptors. A grease trap was defined as, "a device designed to retain grease from one to a maximum of four fixtures." A grease interceptor was defined as, "an interceptor of at least 750 gallon capacity to serve one or more fixtures and which shall be remotely located." The code further added Appendix H, which governed the sizing (and later the installation and design) of commercial kitchen grease interceptors (not grease traps). The code also modified the flow control requirements to stipulate, "each plumbing fixture or piece of equipment connected to a grease trap shall be provided with an approved type flow control or restricting device installed in a readily accessible and visible location in the tail piece or drain outlet of each such fixture." The code retained the previous requirements governing flow control devices.

Beginning with the 1997 edition of the UPC, the code adopted a new format for layout and the same fixture/flow control requirements were placed in section 1014.3, but an exception was added that stated, "Listed grease traps with approved type flow controls or restricting devices may be installed in an accessible location in accordance with the manufacturer's instructions." This was confusing because the requirements stated before the exception clearly stipulated that the flow control or restricting device shall be installed, "in the tail piece or drain outlet" of each fixture or piece of equipment connected to a grease trap. 

The 2000 edition of the UPC made substantial changes to section 1014.3 stating that, "each plumbing fixture or piece of equipment connected to a grease trap shall be provided with an approved type vented flow control installed in a readily accessible and visible location. Flow control devices shall be so designed that the flow through such device or devices shall at no time be greater than the rated capacity of the grease trap. No flow control device having adjustable or removable parts shall be approved. The vented flow-control device shall be located such that no system vent shall be between the flow-control and the grease trap inlet." Here we see that each fixture is to be provided with a vented flow control but the location of the flow control is not stipulated. Previous editions of the code required the flow control device to be installed in the tail piece or drain outlet of each fixture or piece of equipment but never required a vent or air intake on the flow control. This code required a vent on the flow control but also required a vent for the fixture or piece of equipment. The vent on the flow control was not allowed to serve as a fixture vent and no fixture vent could be installed between the flow control and the grease trap, so where was the flow control supposed to be installed? The exception clarified that, "Listed grease traps with approved type flow controls or restricting devices may be installed in an accessible location in accordance with the manufacturer's instructions." Basically the code dumped the problem onto the manufacturers. 

The 2006 edition of the UPC made wholesale changes to everything. First it eliminated the term grease trap and replaced it with a new term 'Hydromechanical Grease Interceptor', defined as, "A plumbing appurtenance or appliance that is installed in a sanitary drainage system to intercept nonpetroleum fats, oil and grease (FOG) from a wastewater discharge and is identified by flow rate, and separation and retention efficiency. The design incorporates air entrainment, hydromechanical separation, interior baffling, and / or barriers in combination or separately, and one of the following:

A - External flow control, with air intake (vent): directly connected
B - External flow control, without air intake (vent): directly connected
C - Without external flow control, directly connected
D - Without external flow control, indirectly connected"

The code also added another new term 'Gravity Grease Interceptor', defined as, "A plumbing appurtenance or appliance installed in a sanitary drainage system to intercept nonpetroleum fats, oils, and greases (FOG) from wastewater discharge and is identified by volume, 30-minute retention time, baffle(s), a minimum of two compartments, a minimum total volume of 300 gallons, and gravity separation." Section 1014.2.1 of the code stipulated that, "each plumbing fixture or piece of equipment connected to a hydromechanical grease interceptor shall be provided with an approved type vented flow control installed in a readily accessible and visible location. Flow control devices shall be so designed that the flow through such device or devices shall at no time be greater than the rated capacity of the grease trap. No flow control device having adjustable or removable parts shall be approved. The vented flow-control device shall be located such that no system vent shall be between the flow-control and the grease trap inlet." Oops, they forgot to replace that last term 'grease trap' with the new term.

So we have this fancy new term and these new types of devices but the same old requirements from previous versions of the code that don't distinguish between the new approved types. What if you have a device 'without' external flow control that is certified and approved for installation? The exception to this section was modified to make an accommodation by stating, "Listed grease interceptors with integral flow controls or restricting devices shall be installed in an accessible location in accordance with the manufacturer's instructions." Unfortunately that didn't really help all that much.

The 2009 edition of the UPC attempted to fix the residual problems with the 2006 edition by modifying section 1014.2.1 to read, "Plumbing fixtures or equipment connected to a Type A and B hydromechanical grease interceptor shall discharge through an approved type of vented flow control installed in a readily accessible and visible location. Flow control devices shall be designed and installed so that the total flow through such a device or devices shall at no time be greater than the rated flow of the connected grease interceptor. No flow control device having adjustable or removable parts shall be approved. The vented flow control device shall be located such that no system vent shall be between the flow control and the grease interceptor inlet."

This definitely did add some clarification, except that Type B hydromechanical devices have an external flow control without air intake (vent). But at least we know which types of devices that the restriction against adjustable or removable parts applies to; namely those with external flow controls, just as it has always been. Those types of hydromechanical grease interceptors without external flow control fall under the exception. The 2012 and 2015 editions of the UPC moved section 1014.2.1 to 1014.2 but the language in the section is the same. 

The sole remaining problem that the code needs to address in this section is a clarification for Type B hydromechanical grease interceptors which do not have a vent or air intake on the external flow control. Since there are no interceptors certified to this type (that I am aware of) there hasn't been any push to proffer a solution to this lingering language issue.



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