If you’ve landed here, chances are you’re either a first-time operator working with an OH1 Type Pump for fluid transfer, a maintenance tech tasked with a routine installation, or someone who’s tried to rig a pump before only to deal with leaks, pressure drops, or premature breakdowns. As a supplier of OH1 Type Pumps, I’ve seen a lot of installation mistakes over the years—errors that turn a reliable piece of equipment into a costly headache. That’s why I put this step-by-step guide together, straight from our on-site service team, to make sure you get the installation right the first time. OH1 Type Pump
First, let’s talk about what an OH1 Type Pump is, just to set context for anyone new to this. The OH1 is a horizontal single-stage end-suction centrifugal pump, designed for general fluid transfer: water, mild chemicals, industrial process fluids, even some slurry applications (as long as it’s within our specified viscosity limits). Its design is compact, energy-efficient, and built to handle continuous operation, but none of that matters if it’s installed wrong. We’ve had customers call us six months post-install saying their pump won’t prime, or it’s vibrating so bad it’s shaking the whole base, and nine times out of ten, the issue traces back to a misstep during installation—not a manufacturing defect.
Let’s start with pre-installation prep. Skipping this step is where most people go wrong. You can’t just pull a pump out of the crate, plop it on a base, and start connecting pipes. First, verify the pump you received is the exact model you ordered. For OH1 Type Pumps, the model number is stamped on the motor housing and the pump casing, and it should match the one on your purchase order. Check for shipping damage: look for dents on the pump casing, bent impeller vanes, loose bolts on the motor, or cracks in the suction and discharge flanges. Even a small dent on the suction side can disrupt flow.
Next, prepare the pump base. The OH1 is designed for rigid, flat mounting, so a flimsy, uneven base is a non-starter. We recommend a concrete base for permanent installations, or a steel base with a minimum thickness of 10mm for temporary setups. The base needs to be level within 0.5mm per meter of length—use a spirit level on both the pump base and the motor base, since these two are aligned during installation. If the base is unlevel, you’ll get misalignment between the pump shaft and motor shaft, which causes excessive wear on bearings and seals. Another pre-install check: make sure the area around the pump is clear for maintenance. You’ll need at least 60cm of space on the suction side for priming, 1m on the discharge side for valve connections, and enough space to access the coupling and seal for routine checks.
Now, mounting the pump. The OH1 is usually supplied as a close-coupled or long-coupled unit. Close-coupled means the pump impeller is directly attached to the motor shaft, no separate coupling. Long-coupled has a separate shaft between the pump and motor, with a flexible coupling to absorb minor misalignment. For either type, the key here is shaft alignment. Misalignment is the number one cause of OH1 pump failures, according to our service data—accounting for 38% of all field issues we respond to.
Start by placing the pump and motor on the base, loosely fastening the anchor bolts at this stage. Don’t tighten them all the way yet. For long-coupled pumps, use a dial indicator to check radial and axial misalignment. Radial misalignment is how much the shafts are off center; we allow a maximum of 0.1mm gap between the two coupling halves. Axial misalignment is how much they’re offset along the shaft; the maximum allowed is 0.05mm. For close-coupled pumps, alignment is simpler: use a straight edge across the motor and motor mounting feet to ensure they’re flat, and check that the motor shaft is parallel to the pump shaft. Once alignment is correct, tighten the anchor bolts in a crisscross pattern—tighten one bolt halfway, then the opposite one, repeating until all are fully torqued. Then recheck alignment, because tightening bolts can shift the base. If alignment is off after tightening, adjust the shims under the motor feet (don’t add shims under the pump feet unless absolutely necessary, as that can affect the impeller’s position in the casing).
Next, piping connections. This is another common area for mistakes that cause poor pump performance. Let’s start with the suction line: the OH1 is an end-suction pump, so the suction line is on one side, discharge on the other. The suction line must be larger in diameter than the pump’s suction flange to reduce friction loss—we recommend a pipe size one size larger for suction lines, same size or one size smaller for discharge lines. Oversized suction lines can cause priming issues, and undersized suction lines create high velocity, which leads to cavitation.
Cavitation is a big one. It happens when the pressure at the pump inlet drops below the vapor pressure of the fluid, forming bubbles that collapse as they move to the higher pressure discharge side. Those collapses cause vibration, noise, and damage to the impeller and casing. To prevent cavitation, the suction line must be airtight—no loose joints, no leaks. Any leaks in the suction line will let air enter, which not only reduces flow but can prevent the pump from priming entirely. Also, install the suction line so it slopes upward toward the pump, at a 1-degree minimum angle. Any low points in the suction line will trap air, making priming impossible. Never install a valve or a reducer on the suction line unless it’s absolutely necessary, and if you do, make sure it’s fully open during operation.
For the discharge line: it should have a gate valve near the pump discharge, for isolating the pump during maintenance, and a check valve further along the line, to prevent backflow when the pump stops. The check valve is important to prevent water hammer, which can damage the pump and pipes. Don’t install any restrictions (like elbows or valves) closer than 1m from the pump discharge, as that can create back pressure and reduce the pump’s flow rate. Also, use flexible connectors (expansion joints) between the pump and pipes to absorb vibration. Without this, the pipes will transfer vibration to the pump, causing wear on bearings and shaft misalignment over time.
Once the piping is connected, it’s time to prime the pump. Priming is the process of filling the pump casing and suction line with fluid to remove air, because centrifugal pumps can’t pump air—they need liquid to create the vacuum that draws in more fluid. For OH1 Type Pumps, most models are self-priming, but that only works if the suction line is airtight and the fluid level is above the pump suction port. Don’t rely on self-priming if you’re handling a fluid that’s easily vaporized; in that case, you’ll need a separate priming pump.
To prime a standard OH1 pump: first, close the discharge valve. Open the vent plug on top of the pump casing, and pour fluid into the casing until it overflows from the vent plug—make sure there are no air bubbles coming out when you pour. Tighten the vent plug firmly, then open the suction valve slightly, and check the suction line for any leaks. If you’re using a pump that requires manual priming, do not skip this step—running the pump dry for even a minute can burn out the mechanical seal, which is a $200 repair on an OH1 pump.
After priming, check the electrical connections. If you’ve got a long-coupled pump, make sure the coupling is properly guarded—this is a safety requirement, not just a convenience. For the motor wiring, double-check the voltage and phase: the OH1 is available in single-phase (for small models, up to 2kW) and three-phase (for larger models, 3kW to 22kW), so the wiring must match the motor’s specifications. A lot of new operators will mix up phase wiring, which makes the motor run in reverse. How do you check rotation? After starting the pump for a few seconds (keep the discharge valve closed for this test), look at the direction of the impeller through the inspection port on the pump casing. The impeller should rotate clockwise when viewed from the motor side. If it’s running counterclockwise, turn off the power immediately, swap two of the three-phase wires, and test again. Running the pump in reverse won’t damage it immediately, but it reduces flow by about 30% and can cause impeller damage over time.
Once rotation is correct, you can start the pump properly. Start by opening the discharge valve slowly, no more than a quarter turn per second. If you open it all the way at once, the sudden flow can cause water hammer, which as I mentioned earlier, is harmful. Monitor the pump’s performance: check the pressure gauge on the discharge line, it should match the OH1’s rated pressure for your model. Listen for any unusual noise: a low humming is normal, but grinding, rattling, or a high-pitched screech means something’s wrong—probably cavitation, misalignment, or impeller damage. Check the pump casing temperature; it should be slightly warmer than ambient, but if it’s hot enough to burn your hand, that’s a sign of excessive friction or overloading.
After the first 24 hours of operation, do a check-in: tighten the anchor bolts again, recheck alignment, and inspect all piping joints for leaks. Routine maintenance checks are also part of long-term success: every month, check the mechanical seal for leaks (a small drip is normal, more than a few drops per minute means the seal needs replacing), every six months, clean the impeller and casing to remove any buildup, and every year, check the alignment and bearing wear.
Now, let’s talk about common mistakes we see that you should avoid at all costs. First, don’t use too much pipe sealant on threaded connections. Pipe sealant is good for sealing, but too much can get into the pump and clog the impeller. Use a thin layer, and wipe off any excess before connecting. Second, don’t neglect the base: a lot of people will use an old, uneven steel plate as a base and wonder why their pump vibrates. Third, don’t run the pump at a flow rate way below or above its rated range. The OH1 is designed to work best at 80-110% of its rated flow; running it at 50% flow for long periods causes overheating, and running it at 120% flow puts too much strain on the motor and impeller.
If you’re installing an OH1 Type Pump, we’ve got a team of experienced technicians who can help you with on-site installation support, or answer any questions you have about the process. Whether you’re replacing an old pump, setting up a new fluid transfer line, or need guidance with a specific application, we’re here to make sure your installation is done right the first time. Don’t let a wrong installation turn your investment into a hassle—reach out to our team to discuss your requirements, get a custom quote, or schedule a pre-installation check. That said, I’m not here to sell to you without context, so if you’re still unsure about any step, even after reading this guide, just get in touch.
Mutistage Water Pump References:
Hydraulic Institute. (2020). Centrifugal Pump Installation and Maintenance Guidelines. National Pump Industry Association.
Grundfos. (2019). OH Series Horizontal End-Suction Pump Installation Manual.
American Society of Mechanical Engineers (ASME). (2021). Standard for Centrifugal Pump Alignment and Vibration.
Hebei Tongda Pump Co., Ltd.
Hebei Tongda Pump Co., Ltd. is well-known as one of the leading oh1 type pump manufacturers and suppliers in China. Our factory offers high quality oh1 type pump made in China with competitive price. Welcome to contact us for pricelist.
Address: No.158, Bo Ming Xi Lu, Boye County, Baoding City, Hebei Province
E-mail: wendy@hbtdby.com
WebSite: https://www.waterpumpmanufacturer.com/
