A deep hole drilling coolant pump that cavitates because of a clogged suction strainer is not just losing flow — it is destroying itself. Cavitation erodes the pump impeller, damages the pump housing, and reduces the pump's ability to deliver high-pressure coolant to the drill tip. The suction strainer is the first line of defense between the coolant tank and the pump — but only if it is the right size, the right mesh, and cleaned on the right schedule.
Strainer Types
Type Comparison
| Strainer Type | Design | Filtration Area | Pressure Drop | Cleaning Method | Best For |
|---|
| Y-strainer | Y-shaped body — screen inside angled leg | Low — screen area = 2–3× pipe area | Moderate | Remove bottom cap — remove screen — clean — reinstall | Small pipes (< 2") — simple systems — low cost |
| Basket strainer | Housing with removable basket — straight-through flow | High — basket area = 5–10× pipe area | Low | Remove cover — lift basket — clean — reinstall | Larger pipes (2–10") — higher flow — easier cleaning |
| Duplex strainer | Two baskets in one housing — diverting valve | High — each basket = 5–10× pipe area | Low | Switch flow to clean basket — clean offline basket — switch back | Continuous operation — no shutdown for cleaning |
| Suction filter (inline) | Cartridge element in housing | High — pleated element area = 10–20× pipe area | Low–Moderate | Replace cartridge element | Fine filtration — high cleanliness requirements |
| Magnetic strainer | Magnetic rod or plate inside housing | N/A (magnetic only) | Very low | Remove magnet — wipe clean | Ferrous chip removal — pre-filtration before fine filter |
| Clean-out strainer | Simple mesh cone inside pipe section | Low — mesh area = 1.5× pipe area | Moderate | Remove clean-out plug — flush debris | Temporary or low-cost installations |
| T-strainer | T-shaped body — screen in vertical leg | Low–Moderate — similar to Y-strainer | Moderate | Remove bottom cap — clean screen | Horizontal pipe runs — larger than Y-strainer |
Strainer Comparison by Application
| Application | Recommended Type | Mesh Size | Material | Special Requirements |
|---|
| Coolant pump suction — general | Y-strainer (small) or basket strainer (large) | 20–40 mesh | Stainless steel screen — cast iron or steel body | Pressure gauge taps before and after |
| High-pressure pump suction | Basket strainer or duplex strainer | 40–60 mesh | Stainless steel screen — ductile iron or steel body | Low pressure drop critical — magnetic insert for ferrous chips |
| Central coolant system — multiple machines | Duplex strainer or automatic self-cleaning | 20–40 mesh | Stainless steel — heavy-duty construction | Continuous operation — automated cleaning option |
| Coolant return line | Y-strainer or T-strainer | 10–20 mesh | Stainless steel screen | Coarse — remove large chips only |
| Magnetic particle removal | Magnetic strainer (in-line) | N/A | Stainless steel body — rare-earth magnet | Install after coarse strainer — before fine filter |
| Make-up water line | Y-strainer | 40–60 mesh | Brass or stainless steel | Protects float valve or solenoid valve |
Mesh Size Selection
Mesh Size Guide
| Mesh Size | Opening Size (µm) | Opening Size (in) | Application | Pressure Drop Impact | Chip Size Captured |
|---|
| 10 mesh | 2000 µm (2.0 mm) | 0.078" | Coarse return lines — tramp material removal | Very low | Large chips — shop debris |
| 20 mesh | 850 µm (0.85 mm) | 0.033" | Standard coolant pump suction — general | Low | Medium chips — coarse swarf |
| 30 mesh | 600 µm (0.60 mm) | 0.023" | Standard pump suction — moderate protection | Low–Moderate | Small chips — coarse fines |
| 40 mesh | 425 µm (0.42 mm) | 0.016" | High-pressure pump suction — better protection | Moderate | Fine chips — coarse grit |
| 60 mesh | 250 µm (0.25 mm) | 0.0098" | Fine filtration pre-filter — precision systems | Moderate–High | Fine particles — sand — grit |
| 80 mesh | 180 µm (0.18 mm) | 0.0070" | Pre-filtration before fine filters | High | Very fine particles |
| 100 mesh | 150 µm (0.15 mm) | 0.0059" | High-cleanliness systems | Very high | Fine silt — small particulate |
Mesh Selection by Pump Type
| Pump Type | Recommended Mesh Size | Why |
|---|
| Centrifugal pump (standard coolant) | 20–30 mesh | Larger clearances — less sensitive to small debris — lower pressure drop allows coarser mesh |
| Centrifugal pump (high-pressure) | 40–60 mesh | Tighter clearances — small debris can damage impeller or block internal passages |
| Gear pump | 40–60 mesh | Tight gear clearances — debris causes scoring and internal leakage |
| Piston pump (axial or radial) | 60–100 mesh | Very tight clearances — debris causes piston scuffing and valve damage |
| Progressive cavity pump | 10–20 mesh | Large clearances — more tolerant of solids — use coarse mesh to minimize pressure drop |
| Submersible pump | 10–20 mesh (integral strainer) | Strainer built into pump — coarser to prevent rapid clogging |
Sizing Guidelines
Strainer Body Size Selection
| Pipe Size (NPS) | Recommended Strainer Body Size | Basket/Y-Strainer Screen Area | Maximum Flow Rate (for 40 mesh) |
|---|
| 1" | 1" (minimum) | 2–3× pipe area | 25 L/min (6 GPM) at 0.1 bar ΔP |
| 1.5" | 1.5" | 2–3× pipe area | 60 L/min (16 GPM) at 0.1 bar ΔP |
| 2" | 2" | 3–5× pipe area | 120 L/min (32 GPM) at 0.1 bar ΔP |
| 3" | 3" | 5–8× pipe area | 300 L/min (80 GPM) at 0.08 bar ΔP |
| 4" | 4" | 5–10× pipe area | 600 L/min (160 GPM) at 0.08 bar ΔP |
| 6" | 6" | 5–10× pipe area | 1,200 L/min (320 GPM) at 0.05 bar ΔP |
Sizing Rules
| Rule | Guideline | Why |
|---|
| Minimum body size | Same as pipe size — never smaller | Smaller body creates excessive pressure drop on suction side |
| Recommended body size | 2× pipe size for suction strainers | Lower velocity through screen — less pressure drop — longer time between cleanings |
| Screen velocity | < 0.5 m/s through screen area at clean condition | Lower velocity reduces pressure drop — reduces tendency for particles to wedge in mesh |
| Pressure drop — clean | < 0.1 bar (1.5 psi) at design flow | Higher clean ΔP means insufficient screen area — will clog faster |
| Pressure drop — change out | 0.3–0.5 bar (5–7 psi) above clean ΔP | ΔP above 0.5 bar on suction side causes pump cavitation risk |
| Safety factor | Screen area 5× pipe area minimum for suction service | Accounts for partial clogging — extends cleaning interval |
Installation Best Practices
| Practice | Detail | Why |
|---|
| Location | Install as close to pump inlet as possible — but with 5–10 pipe diameters of straight pipe before pump | Protects pump from debris — straight inlet pipe ensures proper pump flow |
| Orientation (Y-strainer) | Screen pointing downward or horizontally (not upward) | Debris falls into screen chamber — upward orientation traps air |
| Orientation (basket strainer) | Cover accessible — vertical installation | Basket lifts straight out — debris stays in basket during removal |
| Blow-down valve | Install on Y-strainer bottom cap — small ball valve | Allows quick flush without removing screen — extends interval between screen removals |
| Isolation valves | Valves before and after strainer | Allows strainer cleaning without draining the system |
| Pressure gauge taps | Threaded ports before and after strainer | Differential pressure measurement — ΔP is the primary indicator of strainer condition |
| Bypass line | Optional — for continuous operation during cleaning | Not a substitute for duplex strainer — emergency use only |
| Support | Support strainer body — Y-strainers are heavy | Strainer weight plus pipe stress can damage pump inlet connection |
| Blow-down line routing | Route to drain — not to tank | Blow-down releases concentrated debris — should not return to tank |
Cleaning Procedures
Y-Strainer Cleaning
| Step | Action | Detail |
|---|
| 1 | Close isolation valves before and after strainer | Verify valves fully closed |
| 2 | Open blow-down valve (if equipped) | Relieve pressure — drain coolant from strainer |
| 3 | Place container under strainer cap | Catch residual coolant — approximately 1–2 L for 2" strainer |
| 4 | Remove bottom cap | Use wrench — may be tight — cap contains screen |
| 5 | Remove screen | Pull screen from body — note orientation |
| 6 | Inspect screen | Check for holes — tears — mesh damage — corrosion |
| 7 | Clean screen | Brush with stiff nylon brush under running water — do not use wire brush on stainless mesh |
| 8 | Flush strainer body | Open blow-down valve — flush body with water |
| 9 | Reinstall screen | Correct orientation — fully seated |
| 10 | Apply thread sealant to cap threads | PTFE tape or pipe dope |
| 11 | Reinstall cap | Tighten to snug — do not overtighten |
| 12 | Close blow-down valve | Ensure fully closed |
| 13 | Open isolation valves slowly | Open inlet first — then outlet — check for leaks at cap |
| 14 | Check for leaks | At cap — at blow-down valve — at pressure gauge connections |
| 15 | Record cleaning | Date — ΔP before cleaning — ΔP after cleaning — screen condition |
Basket Strainer Cleaning
| Step | Action | Detail |
|---|
| 1 | Close isolation valves | Before and after strainer |
| 2 | Open vent valve (if equipped) | Relieve pressure — allow air in for draining |
| 3 | Open drain valve | Drain housing |
| 4 | Remove cover bolts | Loosen in cross pattern |
| 5 | Remove cover | Lift straight up — may need lifting device for large covers |
| 6 | Remove basket | Lift by handle — dump contents into waste container |
| 7 | Inspect basket | Check for holes — seam failure — handle condition |
| 8 | Clean basket | Spray with water from inside out — brush if needed — replace if damaged |
| 9 | Inspect gasket or O-ring | Replace if compressed — cut — or damaged |
| 10 | Reinstall basket | Fully seated — centered |
| 11 | Install new gasket/O-ring | Lubricate if needed |
| 12 | Reinstall cover | Cross-bolt pattern — torque to specification |
| 13 | Close drain valve — close vent | Prepare for filling |
| 14 | Open inlet valve slowly | Fill housing gradually — check for leaks |
| 15 | Open outlet valve | Full flow |
| 16 | Check for leaks | At cover — drain — vent — pressure gauge connections |
| 17 | Record cleaning | As per Y-strainer |
Duplex Strainer Switching
| Step | Action | Detail |
|---|
| 1 | Verify clean basket is installed in standby chamber | Confirm — do not assume |
| 2 | Check that standby chamber drain and vent are closed | Open vent or drain will spray coolant |
| 3 | Operate diverting valve | Turn handle to switch flow to clean chamber |
| 4 | Verify flow is established | Check pressure gauges — flow meter |
| 5 | Isolate dirty chamber | Close vent if open — prepare for cleaning |
| 6 | Open drain and vent on dirty chamber | Relieve pressure — drain coolant |
| 7 | Remove cover — remove basket | Clean per basket procedure |
| 8 | Store clean basket in standby | Ready for next switch |
| 9 | Record cleaning and switching | Date and time |
Monitoring
| Monitoring Method | What It Detects | Equipment | Setpoint / Threshold | Response Time |
|---|
| Differential pressure gauge | ΔP across strainer — indicates clogging | Dual-pointer gauge or two gauges | Clean ΔP baseline — clean when ΔP exceeds 2× baseline | Direct reading — immediate |
| Pump suction pressure gauge | Pressure at pump inlet — low pressure indicates strainer blockage | Pressure gauge at pump inlet | Minimum suction pressure per pump spec (typically 0.3 bar absolute) | Direct reading — immediate |
| Pump discharge pressure | Low discharge pressure — may indicate suction restriction | Pressure gauge at pump outlet | Compare to baseline — > 10% drop → investigate | Direct reading — immediate |
| Pump motor current | Reduced current indicates reduced pump load from cavitation | Ammeter on pump motor | Compare to baseline — > 10% drop → investigate | Real-time |
| Pump noise (cavitation) | Crackling or rumbling sound from pump | Listening — acoustic sensor | Any cavitation noise → check strainer | Real-time |
| Visual — sight glass | Coolant flow — bubble indication | Sight glass in pump supply line | Bubbles indicate cavitation → check strainer | Immediate |
| Timer-based cleaning schedule | N/A — assumes clogging rate is consistent | N/A | Clean per schedule (daily, weekly) | Fixed interval — no feedback |
| Automatic strainer cleaning cycle | N/A — self-cleaning | Motorized strainer with backwash | Automatic at ΔP setpoint or timer | Automatic |
Common Problems
| Problem | Likely Cause | Corrective Action | Prevention |
|---|
| Rapid strainer clogging (hours instead of days) | High chip load — large chips — tank chip settling inadequate | Clean strainer — check chip conveyor — improve tank chip settling | Increase tank volume for settling — install chip conveyor — pre-filter return |
| Strainer mesh corroding / failing | Incorrect mesh material — coolant chemistry attacking screen | Replace with stainless steel 316 mesh — verify coolant compatibility | Use 316 stainless for all coolant strainers — verify chemistry |
| Cavitation at pump with clean strainer | Strainer undersized — mesh too fine — pump oversized for suction conditions | Increase strainer size (2× pipe size) — use coarser mesh (20–30) | Size strainer per guidelines — verify NPSH available |
| Strainer bypass valve leaking | Debris on seat — worn seal — corrosion | Clean or replace bypass valve | Inspect bypass during strainer cleaning |
| Gasket / cover leak after cleaning | Gasket damaged — cover not torqued properly — surface damage | Replace gasket — re-torque cover — inspect sealing surface | Replace gasket at each cleaning — torque per spec |
| Y-strainer cap leak | Cap gasket damaged — cross-threaded — over-tightened | Replace cap gasket — inspect threads — lubricate | Hand-tighten then 1/4 turn with wrench — do not overtighten |
| Duplex valve difficult to operate | Debris in valve — handle linkage binding — valve seat damage | Clean valve — lubricate linkage — rebuild valve | Operate duplex valve weekly to keep mechanism free |
| Magnetic strainer not collecting chips | Magnet saturated — magnet weak — flow bypassing magnet | Clean magnet — replace with stronger magnet — verify flow path | Clean magnetic strainer daily — verify effectiveness monthly |
FAQ
What is the purpose of a suction strainer on a deep hole drilling coolant pump?
The suction strainer protects the coolant pump by capturing debris — metal chips, swarf, scale, and shop debris — before they enter the pump. Without a suction strainer, debris can: damage the pump impeller (chipping or eroding the vanes — reducing pump performance permanently), clog internal pump passages (restricting flow — reducing pressure — causing overheating), score close-clearance surfaces (wear rings, bushings, and internal seals — increasing internal leakage and reducing pump efficiency), and travel downstream to block coolant supply lines and solenoid valves. The suction strainer is a coarse filter (typically 20–60 mesh — capturing particles > 250–850 µm) — it does not provide fine filtration. It catches the large debris that would quickly destroy a pump or clog a system. Fine filtration (5–20 µm) is handled by separate pressure-side filters downstream of the pump.
What mesh size should I use for a coolant pump suction strainer?
Mesh size depends on pump type: standard centrifugal coolant pump — 20–30 mesh (captures particles > 600–850 µm — low pressure drop — adequate protection for standard pumps with relatively large internal clearances). High-pressure centrifugal pump — 40–60 mesh (tighter internal clearances — smaller debris can cause damage — 40 mesh is a good balance of protection vs pressure drop). Gear pump — 40–60 mesh (gear teeth mesh tightly — debris causes scoring and internal leakage — finer mesh is justified). Piston pump — 60–100 mesh (very tight clearances between pistons and bores — any abrasive particle causes rapid wear). In all cases: use the coarsest mesh that provides adequate pump protection — finer mesh increases pressure drop and clogs faster. A 40-mesh strainer captures particles > 425 µm while maintaining acceptable pressure drop for most systems. Use 316 stainless steel mesh for corrosion resistance.
How do I know when the suction strainer needs cleaning?
The primary indicator is differential pressure (ΔP) across the strainer: measure pressure before and after the strainer using pressure gauges or a differential pressure gauge. Record the clean ΔP (baseline — typically < 0.1 bar for a properly sized strainer). Clean the strainer when ΔP reaches 2–3× the clean baseline or 0.3–0.5 bar absolute — whichever comes first. Secondary indicators: pump suction pressure dropping below the pump manufacturer's minimum requirement (typically 0.3 bar absolute for centrifugal pumps — lower than this causes cavitation). Pump noise changes — cavitation sounds (crackling, rumbling, or popping from the pump) indicate suction restriction. Pump discharge pressure dropping (less flow through the pump because the suction is starved — discharge pressure drops > 10% below normal). For systems without pressure gauges: clean the strainer on a fixed schedule based on experience (daily for heavy chip loads — weekly for clean systems — and adjust based on observed condition).
How often should suction strainers be cleaned?
Cleaning frequency depends on chip load, chip size, and system design: heavy chip load (cast iron, continuous operation, poor chip settling) — clean daily or every shift — the strainer catches significant debris rapidly. Medium chip load (steel, moderate production, decent chip settling) — clean weekly — the strainer catches moderate debris. Light chip load (aluminum, low production, well-designed chip settling) — clean monthly — the strainer catches minimal debris. Best practice: start with a higher frequency (weekly for medium systems) and adjust based on ΔP monitoring. If ΔP after one week is still near baseline — extend to two weeks. If ΔP reaches 0.5 bar after three days — clean more frequently. Install pressure gauges and clean based on ΔP rather than a fixed schedule — this optimizes cleaning frequency and catches unexpected chip loads before they cause pump cavitation.
What happens if I use the wrong mesh size or strainer type?
Using the wrong mesh: too fine (e.g., 100 mesh on a large centrifugal pump) — high pressure drop — rapid clogging — pump cavitation — reduced coolant flow — possible pump damage from cavitation. Too coarse (e.g., 10 mesh on a piston pump) — large debris passes through the strainer — debris enters the pump — internal damage — scoring — valve damage — pump failure. Using the wrong strainer type: Y-strainer on a large-diameter suction line (> 3") — inadequate screen area — high ΔP — cavitation risk — Y-strainers are for small pipes only. Basket strainer on a 1" line — oversized — acceptable but more expensive than necessary. The correct selection: match strainer type to pipe size, match mesh size to pump type, and ensure stainless steel construction for coolant compatibility. Never install a suction strainer without a pressure gauge — you cannot manage what you cannot measure.
The suction strainer is a simple component that performs a critical function — protecting the coolant pump from debris damage. Select the right type (Y-strainer for small pipes, basket for large, duplex for continuous operation), the right mesh (20–40 for standard pumps, 40–60 for high-pressure, 60–100 for piston pumps), and the right size (2× pipe size for minimum ΔP). Install pressure gauges before and after the strainer — clean based on ΔP, not a guess. A clean strainer with low ΔP means the pump is getting full flow — and the coolant system is delivering the pressure and flow the drilling process needs. A clogged strainer that is not cleaned will destroy a pump. This article reflects industry practice as of 2026.
