User Guide

2
Feature and Operating Procedures
MAINTENANCE MANUAL MODELS 805YD, 806YD 2
1
/2"- 10" (65 – 250mm)
Double Check Valves and Double Check
Detector Assemblies
This device consists of two independently operating poppet type check
valves. Each check valve is spring loaded to maintain a minimum of 1
PSIG differential pressure across the check in a no-flow condition. In
a normal-flow condition the checks open an amount corresponding to
the flow rate. During a backflow (backpressure) situation, the seat discs
close and seal to prevent any flow reversal. Sizes 2
1
⁄2" through 10" (65 –
250mm) (805YD) include two spring loaded Y-pattern check valves with
epoxy coated ductile iron bodies and bronze trim, two cast iron shutoff
valves and four test-cocks for field testing. All valves are flanged type, and
the unit is shipped completely assembled.
The Model 806YD device consists of a mainline double check valve with
a metered
3
⁄4" by-pass double check valve connected around the mainline
checks. The mainline pressure drop is slightly higher than the by-pass,
thus all small flow up to the crossover point (3 gpm minimum) is through
the by-pass. Above the crossover point flow is through the mainline and
the by-pass.
The FEBCO 806YD device main line unit consists of two independent,
spring loaded, Y-pattern check valves, two shutoff valves and four test-
cocks. The spring loaded poppets in conjunction with soft elastomer discs
provide drip tight closure against backflow. The Y-pattern valve design
provides low pressure loss at the high flow rates. The shutoff valves
are OS&Y type, UL listed for fireline service. The by-pass line assembly
consists of a water meter in series with a Model 805YB
3
⁄4" double check
valve. The meter is the total type with accurate registration between 1
and 20 gpm flow rates. The static pressure drop across both checks is
approximately 2psi less than the mainline check valves.
Consult local codes before installing any Backflow Prevention assembly.
General Service Procedures
(General service instructions applicable to all sizes.)
1. Rinse all parts with clean water prior to assembly.
2. DO NOT USE ANY PIPE DOPE, OIL, GREASE OR SOLVENT ON ANY
PARTS unless instructed to do so.
3. Do not force parts. Parts should fit freely together. Excess force may
cause damage and render the device inoperable.
4. Carefully inspect seals, seating surfaces, etc. for damage or debris.
5. Test unit after servicing to ensure proper operations.
6. Refer to applicable parts list and figures for more information.
7. A table on the back page provides size and material information for
standard parts (non-special design). These parts can usually be pur-
chased locally from parts distributors, rather than special order from
the factory.
8. Some water conditions can cause a buildup of calcium or similar mate-
rial deposits on some moving parts. Normally this condition would not
occur on devices used in systems with varying flow rates. The scrap-
ing action of moving parts helps to remove any deposits. However,
with devices used on static systems such as firelines, any deposits
would not be scraped away and could interfere with the check valve
operation. Devices in these applications should be disassembled and
inspected on a periodic basis depending on water quality. Any deposits
should be removed from the center guiding stem and bushings. Use
care to avoid damage to guiding surfaces.