8 replies to this topic

[shantanu.ghag]

Dear all, 

 

Few query related PDS of flow elements, 

 

1. Can anyone suggest allowable DP criteria for flow element-orifice?

    As a general criteria, i think it is below 0.2 bar, but in some data sheet i have seen its varying w.r.t.                      min/normal/max flow also.

2. Also, how min/max flow in data sheet is decided over normal flow rate? is it specific % of normal flow rate?

3. How can we decide maximum meter range?

 

Thanks, 

Shantanu.

[Technical Bard]

An orifice plate will generally be specified for 100, 200 or 400 inH2O pressure drop measured by the taps, but some of that is recovered.  Then you need to consider the pressure drop of the meter run (if you are installing a proper meter run of straight pipe).  A typical allowable pressure drop across an orifice meter would be 1-2 psi.  Other meter types are generally more (except ultrasonics).

[shantanu.ghag]

An orifice plate will generally be specified for 100, 200 or 400 inH2O pressure drop measured by the taps, but some of that is recovered.  Then you need to consider the pressure drop of the meter run (if you are installing a proper meter run of straight pipe).  A typical allowable pressure drop across an orifice meter would be 1-2 psi.  Other meter types are generally more (except ultrasonics).

Thanks, Technical Bard! I am looking from process point of view. 1. what will be max DP considered during design?

2. criteria for min/max flow considered  3. transmitter max flow consideration criteria.

Thanks, 

Shantanu.

[Chemitofreak]

Dear all, 

 

Few query related PDS of flow elements, 

 

1. Can anyone suggest allowable DP criteria for flow element-orifice?

    As a general criteria, i think it is below 0.2 bar, but in some data sheet i have seen its varying w.r.t.                      min/normal/max flow also.

 

Generally, if the orifice is in the pump circuit the pressure drop for the rated flow is assumed as 0.25 bar. For vapour line, it can be less, based on the pressure available in the system.

 

2. Also, how min/max flow in data sheet is decided over normal flow rate? is it specific % of normal flow rate?

 

Max Flow = Design Margin x Normal Flow

 

Min Flow = Based on the turndown of the plant which can be 20 to 30%

 

3. How can we decide maximum meter range?

 

Once you get the max and min flow, you get the range.

 

Thanks, 

Shantanu.

[Bodhisatya]

Dear all, 

 

Few query related PDS of flow elements, 

 

1. Can anyone suggest allowable DP criteria for flow element-orifice?

    As a general criteria, i think it is below 0.2 bar, but in some data sheet i have seen its varying w.r.t.                      min/normal/max flow also.

2. Also, how min/max flow in data sheet is decided over normal flow rate? is it specific % of normal flow rate?

3. How can we decide maximum meter range?

 

Thanks, 

Shantanu.

1. Standard dP calibration ranges are : 25,50,100,150 in H20.Depending upon the state of your liquid (Saturated or subcooled) dP will change,for Gases depending upon pressure dP needs to be fixed.

2. Hydraulics calculation or customer preference gives you the turn-up and turn-down flow rate.

3. Thumb of Rule we follow in our organization: Roughly, Normal Flow Rate *1.25 as the METER MAX, this typically gives a Normal flow rate reading as 80 % of full scale.

 

Regards

Bodhisatya.

[shantanu.ghag]

 

Dear all, 

 

Few query related PDS of flow elements, 

 

1. Can anyone suggest allowable DP criteria for flow element-orifice?

    As a general criteria, i think it is below 0.2 bar, but in some data sheet i have seen its varying w.r.t.                      min/normal/max flow also.

 

Generally, if the orifice is in the pump circuit the pressure drop for the rated flow is assumed as 0.25 bar. For vapour line, it can be less, based on the pressure available in the system.

 

2. Also, how min/max flow in data sheet is decided over normal flow rate? is it specific % of normal flow rate?

 

Max Flow = Design Margin x Normal Flow

 

Min Flow = Based on the turndown of the plant which can be 20 to 30%

 

3. How can we decide maximum meter range?

 

Once you get the max and min flow, you get the range.

 

Thanks, 

Shantanu.

Thanks. 0.25 bar is allowable Dp? does this change with min/normal/max flow rate?

 

[shantanu.ghag]

 

Dear all, 

 

Few query related PDS of flow elements, 

 

1. Can anyone suggest allowable DP criteria for flow element-orifice?

    As a general criteria, i think it is below 0.2 bar, but in some data sheet i have seen its varying w.r.t.                      min/normal/max flow also.

2. Also, how min/max flow in data sheet is decided over normal flow rate? is it specific % of normal flow rate?

3. How can we decide maximum meter range?

 

Thanks, 

Shantanu.

1. Standard dP calibration ranges are : 25,50,100,150 in H20.Depending upon the state of your liquid (Saturated or subcooled) dP will change,for Gases depending upon pressure dP needs to be fixed.

2. Hydraulics calculation or customer preference gives you the turn-up and turn-down flow rate.

3. Thumb of Rule we follow in our organization: Roughly, Normal Flow Rate *1.25 as the METER MAX, this typically gives a Normal flow rate reading as 80 % of full scale.

 

Regards

Bodhisatya.

 

Thanks Bodhisatya. i have seen process data sheet in which meter maxx is ~1.44 times of normal flow hence looking for any such design criteria. Thanks.

[Chemitofreak]

 

 

Dear all, 

 

Few query related PDS of flow elements, 

 

1. Can anyone suggest allowable DP criteria for flow element-orifice?

    As a general criteria, i think it is below 0.2 bar, but in some data sheet i have seen its varying w.r.t.                      min/normal/max flow also.

 

Generally, if the orifice is in the pump circuit the pressure drop for the rated flow is assumed as 0.25 bar. For vapour line, it can be less, based on the pressure available in the system.

 

2. Also, how min/max flow in data sheet is decided over normal flow rate? is it specific % of normal flow rate?

 

Max Flow = Design Margin x Normal Flow

 

Min Flow = Based on the turndown of the plant which can be 20 to 30%

 

3. How can we decide maximum meter range?

 

Once you get the max and min flow, you get the range.

 

Thanks, 

Shantanu.

Thanks. 0.25 bar is allowable Dp? does this change with min/normal/max flow rate?

 

 

The delta P across the orifice increases when the flowrate increases. When there is less flow, there is less delta P.

 

The 0.25 bar that we are talking about is at the rated case.

[Bodhisatya]

 

 

 

Thanks Bodhisatya. i have seen process data sheet in which meter maxx is ~1.44 times of normal flow hence looking for any such design criteria. Thanks.

 

There ain't any design criteria, bigger the range, more money u need to shell out. Higher Meter Max will bring error if the turndown flowrate is low. Select Meter Max as such, Normal Flow rate is 80 % at full scale, Max at around 90 % and Minimum not less than 35 % of full scale.

 

Bodhisatya.