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INSTALLATION AND SERVICE INSTRUCTION

Siemens Industry, Inc.

 

 

1

 
 

SD62 

 

Rev 11 

 

March 2011 

 

Supersedes Rev 10 

 

Model Series 62 Constant Differential Relay 

 

INTRODUCTION 

 
The Constant Differential Relay maintains a constant pressure drop across an internal needle valve for any flow 
setting up to about 2.1 cubic feet of air per hour. It thus provides a means for maintaining a practically constant 
volumetric rate of flow regardless of variations of the process or supply pressures. The differential maintained across 
the needle valve is 1 to 2 psig. This permits a greater opening of the needle valve, thus making it less subject to 
clogging. The constant differential relay may be used in conjunction with a rotameter type indicator. 
 
The differential applied to the internal needle valve is determined by a spring-loaded diaphragm in the constant 
differential relay. This diaphragm controls the action of a valve plunger to automatically admit supply air to the 
needle valve at the required rate. A self-contained automatic bleed discharges excess supply air to the atmosphere 
when necessary. The constant differential relay is made of aluminum, brass, stainless steel, Neoprene and Buna-N. 
The rotameter is constructed of aluminum, stainless steel, borosilicate glass, Buna-N (O-rings), ruby sapphire (float) 
and brass (fittings). Neither will be affected by ordinary air line impurities. 
 
This instruction has five major sections: Introduction, Installation, Operation, Maintenance, and Parts List. 
 

Model Designation 

 

 

 

 

62 

Constant Differential Relay 

With Built-In Needle Valve 

Needle Valve with Tight Shut-Off 

Attached Rotameter Piped Assembly 

 

Specifications 

 
Supply Pressure 
 

Minimum................................. At least 5 psig greater than the maximum downstream pressure. 

 Maximum ................................ 150 

psig 

 
Purge Rate: 

 

Models 62V & 62VA 

Models 62VN & 62VNA 

Maximum 

2.1 SCFH 

991 SCCM 

1.8 SCFH 

850 SCCM 

Minimum 

0.9 SCFH 

425 SCCM 

0.06 SCFH 

28 SCCM 

 
Ambient Temperature Limits ................ -40° to +180°F (-40° to +82°C) 
 
 

Summary of Contents for 62 Series

Page 1: ...s diaphragm controls the action of a valve plunger to automatically admit supply air to the needle valve at the required rate A self contained automatic bleed discharges excess supply air to the atmosphere when necessary The constant differential relay is made of aluminum brass stainless steel Neoprene and Buna N The rotameter is constructed of aluminum stainless steel borosilicate glass Buna N O ...

Page 2: ...e kept as short as possible and should be at least 1 4 pipe or larger For example At a flow rate of 0 9 SCFH the pressure drop in a 20 foot length of 1 4 pipe will not exceed 0 20 H20 head but approximately ten times this drop would be obtained with 1 4 O D tubing Pressure drop between the relay and the junction of the receiving instrument is ordinarily of no consequence so that this line may be m...

Page 3: ...SD62 Figure 1 Installation Dimensions with Rounded Rotameter 3 ...

Page 4: ...e instrument should be no larger than 3 microns Dew Point The dew point at line pressure should be at least 10 C 18 F below the minimum temperature to which any part of the instrument air system is exposed at any season of the year Under no circumstances should the dew point at line pressure exceed 2 C 35 6 F Oil Content Maximum total oil or hydrocarbon content exclusive of non condensable should ...

Page 5: ...nated This permits flows of less than 0 9 SCFH It is recommended that a flow indicator be used in the downstream line since it is possible to shut this unit off completely MAINTENANCE The use of a Constant Differential Relay greatly reduces the maintenance ordinarily required with the conventional purging or bubbling system The rate of flow of the purging gas can be expected to remain constant ove...

Page 6: ...elect the product line e g Control Solutions Warranty The sales contract contains the entire obligation of Siemens The warranty contained in the contract between the parties is the sole warranty of Siemens Any statements continued herein do not create new warranties or modify the existing warranty All product designations may be trademarks or product names of Siemens Industry Inc or other supplier...

Page 7: ...ly 1 12 1145 19 Mounting Bracket 1 13 7135 19 Diaphragm 1 14 8912 10 Retaining Screw Model 62VN only 1 15 2155 225 Filter Screen 2 A6X30060272 Rotameter Rounded Not shown A Models only Supersedes the following part 1 12431 11 Rotameter Rectangular Not shown A Models only Discontinued part A 1 3345 1 4 20 x 7 8 Lg Fil HD Screw 3 B 1 3410 1 4 20 x 1 Lg Fil Hd Screw 3 C 1 7303 1 4 Med Lockwasher 6 Re...

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