10 Grit Hopper Obstruction
Grit production below 160 gpm may indicate an obstruction in the grit system. A typical obstruction occurs in one of the grit hoppers, but can also occur in the grit piping or in a grit pump.
This SOP provides the operator with a methodical procedure for locating and dislodging an obstruction in the grit system.
Open valves on the pressurized Recycle Water System slowly.
- Ensure that grit pumps are complete shut down before backflushing.
- Ensure that the grit flow sensor and transmitter are calibrated and do not provide a false flow rate.
- It may not be possible to properly isolate the hopper(s) if the obstruction is located in one of the isolation valves.
Operator I, knowledge of grit system and equipment controls.
- Record activity to log book.
Obstructions in the grit system can occur in the hopper(s), grit piping and/or grit pumps. A typical obstruction occurs in one of the hoppers and its location is determined by isolating each hopper. A more severe obstruction may also require back flushing.
One indication of an obstruction would be low grit production, as displayed at the Grit Transfer Pump Flow Sensor screen {tag no. 1004FE/FIT0674}. Normal production is 160 gpm, so anything lower could be an indication of an obstruction.
Location of the obstruction is generally determined by closing suction valves on the Grit Transfer Suction Header. Each suction valve is associated with one hopper.
Suction Valve Tag No. | Associated Hopper |
1004VLV0677B | Hopper #1 |
1004VLV0677D | Hopper #2 |
1004VLV0677H | Hopper #3 |
1004VLV0677J | Hopper #4 |
1. Isolate hoppers by closing suction valves until the obstruction is located:
a. Isolate hoppers by closing grit suction header valves. Refer to the Suction Valve/Hopper table above. For example, closing valves 1004VLV0677B, 1004VLV0677D, and 1004VLV0667H will isolate Hopper #4.
b. Check the Grit Transfer Pump Flow Sensor screen {tag no. 1004FE/FIT0674} for grit production. If the displayed flow rate is at or near to 160 gpm, go to Step 1.c. If the displayed flow is significantly lower than 160 gpm, go to Step 2.
c. Close another set of valves to isolate a different hopper.
d. Continue closing valves and isolating hoppers until the obstruction is located. When the obstruction is located, go to Step 2.
2. Back flush obstruction with Plant Recycle Water:
a. Open the Recycled Water Hose Bib located in the Grit Pump Room {tag no. 1603VLV6298}. Open slowly since the system is under pressure.
b. Open the Recycled Water Hose Bib located in the Grit Pump Room at the end of the grit suction header {tag no. 1004VLV0677E}. Open slowly since the system is under pressure.
c. Allow the water to run until the obstruction is forced out. If the obstruction won’t flush out, go to Step 3. If the obstruction is flushed, skip Step 3 and go to Step 4.
3. Isolate Grit Pumps from back flushing:
a. Push the E-Stop button {tag nos. 1004HS0100C & 1004HS0200C} to shut down the out of service (lag) Grit Pump {tag nos. 1004PMP/MTR0100 & 1004PMP/MTR0200}.
b. Push the E-Stop button {tag nos. 1004HS0100C & 1004HS0200C} to shut down the in service (lead) Grit Pump tag nos. 1004PMP/MTR0100 & 1004PMP/MTR0200}.
c. After both Grit Pumps have been taken off line, shut both Grit Pump Suction Valves {tag nos. 1004VLV0100 & 1004VLV0200}.
d. Continue allowing Plant Recycle Water to flush the suction header until the obstruction is forced back through the hopper.
e. After the obstruction has been flushed, close the Recycled Water Hose Bib located in the Grit Pump Room at the end of the grit suction header {tag no. 1004VLV0677E}.
f. Close the Recycled Water Hose Bib located in the Grit Pump Room {tag no. 1603VLV6298}.
g. Open both Grit Pump Suction Valves {tag nos. 1004VLV0100 & 1004VLV0200}.
h. Push the E-Stop button {tag nos. 1004HS0100C & 1004HS0200C} to re-start the in service (lead) Grit Pump tag nos. 1004PMP/MTR0100 & 1004PMP/MTR0200}.
i. Push the E-Stop button {tag nos. 1004HS0100C & 1004HS0200C} to re-start the out of service (lag) Grit Pump {tag nos. 1004PMP/MTR0100 & 1004PMP/MTR0200}.
4. Return the grit system to normal operation after the obstruction has been removed.
a. Re-open the closed Grit Transfer Suction Header Valves {tag nos. 1004VLV0677B, 1004VLV0677D, 1004VLV0677H &1004VLV0677J}.
b. Restart the in service (lead) grit pump at the HOA Switch {tag nos. 1004HS0100B & 1004HS0200B}.
c. Restart the out of service (lag) grit pump at the HOA Switch {tag nos. 1004HS0100B & 1004HS0200B}.
- Update log book.
- Update maintenance records (if applicable).
- Report any maintenance or attention that is required.
Grit production of 160 gpm (minimum) indicates that no obstruction is present in the grit system.
Continue isolating hoppers and piping until the obstruction is located and flushed.
EQUIPMENT NAME | TAG NUMBER |
Grit Hopper #1 Suction Valve | 1004VLV0677B |
Grit Hopper #2 Suction Valve | 1004VLV0677D |
Grit Hopper #3 Suction Valve | 1004VLV0677H |
Grit Hopper #4 Suction Valve | 1004VLV0677J |
Grit Transfer Pump Flow Sensor | 1004FE/FIT0674 |
Recycled Water Hose Bib Valve | 1603VLV6298 |
Recycled Water Hose Bib Valve | 1004VLV0677E |
Grit Pump No. 1 | 1004PMP0100 |
Grit Pump No. 1 Motor | 1004MTR0100 |
Grit Pump No. 1 E-Stop Button | 1004HS0100C |
Grit Pump No. 1 HOA Switch | 1004HS0100B |
Grit Pump No. 1 Suction Valve | 1004VLV0100 |
Grit Pump No. 2 | 1004PMP0200 |
Grit Pump No. 2 Motor | 1004MTR0200 |
Grit Pump No. 2 E-Stop Button | 1004HS0200C |
Grit Pump No. 2 HOA Switch | 1004HS0200B |
Grit Pump No. 2 Suction Valve | 1004VLV0200 |