289 series Spring-Loaded Relief Valves0 pages

Bulletin 71.4:289
October 2014

289 Series Spring-Loaded Relief Valves

W1870_1

TYPE 289L

W18701

1 NPT TYPES 289H
AND 289HH
W18702

W1870_2

2 NPT TYPE 289H

TYPES 289U AND 289A

Figure 1. Types 289H, 289L and 289U Relief Valves

Introduction
The 289 Series relief valve is a throttling relief valve
used downstream of pressure regulators to protect the
downstream system from overpressure. A smooth
throttling action minimizes pressure surges in the
system during emergency operation. These relief valves
are available in 1/4, 3/4, 1 or 2 NPT sizes with spring
ranges (relief pressure settings) from 5 in. w.c. to
75 psig / 12 mbar to 5.2 bar.
All sizes above 1/4 NPT feature a pitot tube booster
(Figure 1) for achieving the highest possible relief
capacity with a minimum buildup of system pressure.
When the valve is opening, high gas velocity through
the orifice creates an area of relatively low pressure
near the end of the pitot tube. This pitot tube effect
forms a partial vacuum above the diaphragm which
helps to open the valve.

Features
• Throttling Type Relief—Smooth, sensitive
throttling action minimizes pressure surges.
• High Flow Rates—As shown by the Figure 3
capacity curves, high flow rates can be achieved
with minimum pressure buildup due to the boosting
system which increases the relief valve opening.
• Small Size—The 289 Series relief valves are
small and compact, making them suitable for areas
limited in space.
• Reliability Due to Simplicity—A single
internal assembly decreases the possibility of
mechanical failure.
D100154X012

The relief valve diaphragm functions as a valve disk
to control flow in all types except the Types 289H and
289HH, which use O-ring seats. The Nitrile (NBR)
or Neoprene (CR) seating surfaces provide tight

shutoff. The 289 Series relief valves are ideal for
low-pressure settings due to the increased sensitivity
provided by the large diaphragm area.

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