HHS:PHS:FDA:CFSAN:OFP:DCP:MST
 
      200 C Street, SW
      Washington DC 20204
 
      M-b-335
 
      November 30, 2001
 
 
TO:  		All Regional Food and Drug Directors
      Attn:  Regional Milk Specialists
 
FROM:  	Milk Safety Team (HFS-626)
 
SUBJECT:  	Break to Atmosphere Twin Tanks
 
 
The Break to Atmosphere Twin Tanks has been reviewed and found to comply with
the applicable provisions of the Grade A Pasteurized Milk Ordinance (PMO) when
used as an atmospheric break between raw and pasteurized milk and milk products.
 
Compliance with the PMO is based upon construction, installation and operation
in conformance with the attached drawing and operating description as well as
the following criteria from the NCIMS Technical Committee, addressed in the
solution to Proposal 119, passed at the 2001 NCIMS Conference:
 
The distance between the overflow level of the lower balance tank and the outlet
of the outlet control valve on the upper balance tank must be the greater of the
liquid column height of the lower balance tank plus two times the diameter of
the pipeline connecting the upper and lower balance tanks or 28 inches plus two
times the diameter of the pipeline connecting the upper and lower balance tanks.
Additionally, the plug on the control valve shall be grooved to prevent complete
closure of the valve.
 
For further information contact:
 
      Warren Taylor
      Warren Taylor Services, Inc.
      37444 Holley Road
      Pomeroy, Ohio 45769
      Phone: (740) 992-7992
      Fax: (740) 992-7994
      E-mail: WTSPRO@aol.com
 
 
FDA's review and acceptance of this equipment, does not constitute agency
endorsement or approval. Any representation on a label or in printed literature
citing or indicating as, "FDA Approved" is false and misleading.
 
Copies of this memorandum are enclosed for distribution to Regional Milk
Specialists, State Milk Regulatory Agencies and State Milk Sanitation Rating
Officers in your region. This memorandum will also be available on the FDA Web
site at http://www.cfsan.fda.gov at a later date and should be widely
distributed to representatives of the dairy industry and other interested
parties.
 
 
 
 
 
							
      Steven T. Sims
							FDA/MST Milk Sanitation Officer
 
 
 
Attachments:
Drawings 1-7
   Operating Description
 
 
 
 
 

 
 
 
WARREN TAYLOR SERVICES, INC.
	37444 Holley Road         Pomeroy, Ohio  45769   USA
	Tel:(740)992-7992   Fax: 992-7994  E-mail: WTSPRO@aol.com	
								
                                                       November 1, 2001
 
Operating Description
Break To Atmosphere Twin Tanks
 
 
The Problem - To provide absolute separation of pasteurized product and product
contact surfaces, such as HTST systems and discharge piping, from raw product,
piping, and equipment, to which pasteurized product must be transferred.
 
By regulatory code this requires a break to atmosphere, which has typically been
met by providing a tank in which the inlet drops product well above the product
level.  The resulting splash and turbulence of product and air causes foaming,
particularly when skim milk is transferred.
 
Foaming lends to numerous problems including product loss, poor homogenization
efficiencies, burn on in HTST plates during reprocessing, and increased
temperatures and microbiological activity.
 
The Solution - A unique Twin Break Tank arrangement in which pasteurized product
is bottom fed into an elevated HTST type balance tank ("Top Tank") and allowed
to flow by gravity into a similar lower balance tank ("Bottom Tank"), again
bottom fed.
 
Since both tanks are vented vessels which are constructed so they cannot be
pressurized or under vacuum, it is not possible for raw product to back feed
under pressure beyond the bottom tank overflow opening.  It is also not possible
for raw product to be drawn by vacuum up into the top tank.  In this way, raw
product cannot possibly migrate back to the pasteurized side and contaminate
pasteurized product or product contact surfaces.  At the same time, pasteurized
product transferred to the raw side through the Break Tank(s) is bottom filled
into each tank, minimizing product/air mixing and foaming problems.
 
The Details - Refer to the attached drawings 2029-01, 02, 03, 04, 05, 06 and 07
which show the system requirements and operation.
 
Overview - The system can be piped into an existing operation.  Its controls are
best integrated with the existing HTST and raw destination tank controls to
reduce the possibility of product loss due to HTST recycle or divert, or raw
destination tanks overflowing.  This also makes it possible to provide automatic
Break Tank emptying and associated line air blowing to minimize product losses,
and automatic CIP sequencing to assure consistent cleaning.
 
A self contained control system can be provided for integration with existing
controls or  in the case of facilities with computer or programmable controller
type controls, the existing plant control system can be used to provide the
necessary automation.
 
Level is maintained in Break Tanks above the side inlet level to prevent
foaming.  Level is controlled in the top tank by modulating the control valve
between the tanks.   Level is maintained in the bottom tank by controlling the
rate that product is pumped away by the removal pump.  This can be done either
with a throttling valve on the removal pump discharge or by controlling the
motor speed with a variable frequency drive.
 
Operational Control Description - There are three distinct modes of operation:
1. Process
2. Pumpout/Airblow
3. CIP
 
1.  Process Mode - The Break Tanks are empty following CIP cleaning until
product is introduced into them.  When product is first introduced, the level
controllers act to fill the tanks, not operating the removal pump and holding
the control valve closed. Once the top tank level reaches setpoint, the control
valve will begin to open, dropping product down to the bottom tank until the
setpoint level is reached there.  The removal pump will then start, pumping
product out at the same rate it is entering the Break Tanks.
 
This operation will continue until the transfer is completed.  At that time an
automatic or manually initiated pumpdown/airblow sequence can operate to
thoroughly empty both Break Tanks and the transfer lines.
 
2.  Pumpdown/Airblow Mode - After the transfer is completed, as indicated by the
closure of the HTST discharge valve to the Break Tank, the level control of the
top tank is stopped to allow the control valve to open and allow all product to
flow to the bottom tank.  After a preset time which will be determined by the
particular plant's HTST discharge piping, the HTST discharge airblow can be
activated to purge the line of product to the top tank.
 
The control valve will remain open so the top tank will be allowed to completely
drain.
 
 
The removal pump continues to operate under level control, maintaining setpoint
level.  Once the top tank is empty the level control of the bottom tank is
stopped with the removal pump operating for an adjustable time delay after the
bottom tank has reached low level.
 
The bottom tank outlet valve airblow is then activated in combination with the
other plant valves on the way to the destination tank(s) to purge the transfer
lines.
 
3.  CIP Mode - The Break Tanks can be cleaned in a line circuit with flow rates
in the range of 80 to 140 GPM, or in a dedicated Break Tank circuit.  The CIP
supply valves are cycled to spray the tanks during part of the circuit, with
flow also cycled through the normal product piping.  At the end of the cycle the
tanks are pumped down, as in a typical tank CIP cycle.
 
Level Controls - The Break Tank level controls for each tank are similar in
operating modes and functions.  Both tanks are equipped with analog level
sensors which may be pneumatic diaphragm, electronic pressure sensor, or
capacitance type.  There are two discrete alarm setpoints ("low" and "high") in
addition to the "operating level setpoint".
 
System operating responses are listed below.
 
Top Tank			System Response
 
High Level			Process:  Stop the source, typically recycle the HTST.
  (about 24")			Pumpdown/Airblow:  Stop the source airblow.
				CIP:  None.
 
Operate Level                   Process:  Control valve modulated to maintain.
  (about 12")			Pumpdown/Airblow:  None.
				CIP:  none
 
Low Level			Process:  None.
  				Pumpdown/Airblow:  None.
				CIP:  none
 
Bottom Tank			System Response
 
High Level			Process:  Close the control valve and sound alarm.
  (about 24")			Pumpdown/Airblow:  Close the balance valve until high
                                     level signal is lost.
				CIP:  None, except sound alarm.
 
 
Operate Level                   Process:  Removal pump rate modulated to maintain.
  (about 12")			Pumpdown/Airblow:  None.
				CIP:  Removal pump rate modulated to maintain.
 
Low Level                     Process:  Stop removal pump and close bottom tank outlet valve.
  				Pumpdown/Airblow:  Start the time delay before closing the
                                       bottom tank outlet valve and starting the airblow.
				CIP:  Stop the removal pump and close the bottom tank
 						outlet valve.
 
Specific Installation Variations - Variations of tank sizes, piping
configurations, and controls are possible as long as the basic principals of the
system are maintained.
 
 
 
 
 
 
 
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M-b-335	1	November 30, 2001